AB6 family designer ligands of TGF-β superfamily

ABSTRACT

A non-naturally occurring chimeric polypeptide having an activity provided by a TGF-beta family member is disclosed. The chimeric polypeptide of an embodiment comprises two or more domains or fragments from parental TGF-beta proteins operably linked such that the resulting polypeptide is capable of modulating a pathway associated with a TGF-beta family member. In one embodiment, the pathway is a SMAD or DAXX pathway.

TECHNICAL FIELD

The present invention relates to chimeric polypeptide having TGF-betaactivity, nucleic acid encoding the polypeptide, and host cell forproducing the polypeptide.

BACKGROUND ART

Activins and Bone Morphogenetic Proteins (BMPs) are members of a muchlarger Transforming Growth Factor-beta (TGF-β) superfamily of ligands(also called TGF-β ligands). Due to their pervasiveness in numerousdevelopmental and cellular processes, TGF-β ligands have been the focusof great interest.

DISCLOSURE OF INVENTION Technical Problem

For TGF-β ligands to be successfully used as therapeutic tools, severalhurdles need to be overcome. The ability to specifically modify andalter the properties of TGF-β ligands, as well as generate those ligandsin significant quantities is required.

Solution to Problem

1. A chimeric polypeptide which has at least 95% sequence identity to anamino acid sequence comprising a first, a second, a third, a fourth, afifth, and a sixth domains of amino acid residues, wherein the firstdomain of amino acid residues is selected from a group consisting ofamino acid residues 1 to X_(1b) of SEQ ID NO:2, amino acid residues 1 toX_(1aa) of SEQ ID NO:4, amino acid residues 1 to X_(1ab) of SEQ ID NO:6,amino acid residues 1 to X_(1ac) of SEQ ID NO:8, and amino acid residues1 to X_(1ac) of SEQ ID NO: 10; the second domain of amino acid residuesis selected from a group consisting of amino acid residues X_(1b) toX_(2b) of SEQ ID NO:2, amino acid residues X_(1aa) to X_(2aa) of SEQ IDNO:4, amino acid residues X_(1ab) to X_(2ab) of SEQ ID NO:6, amino acidresidues X_(1ac) to X_(2ac) of SEQ ID NO:8, and amino acid residuesX_(1ae) to X_(2ae) of SEQ ID NO: 10; the third domain of amino acidresidues is selected from a group consisting of amino acid residuesX_(2b) to X_(3b) of SEQ ID NO:2, amino acid residues X_(2aa) to X_(3aa)of SEQ ID NO:4, amino acid residues X_(2ab) to X_(3ab) of SEQ ID NO:6,amino acid residues X_(2ac) to X_(3ac) of SEQ ID NO:8, and amino acidresidues X_(2ae) to X_(3ae) of SEQ ID NO: 10; the fourth domain of aminoacid residues is selected from a group consisting of amino acid residuesX_(3b) to X_(4b) of SEQ ID NO:2, amino acid residues X_(3aa) to X_(4aa)of SEQ ID NO:4, amino acid residues X_(3ab) to X_(4ab) of SEQ ID NO:6,amino acid residues X_(3ac) to X_(4ac) of SEQ ID NO:8, and amino acidresidues X_(3ae) to X_(4ae) of SEQ ID NO: 10; the fifth domain of aminoacid residues is selected from a group consisting of amino acid residuesX_(4ab) to X_(5b) of SEQ ID NO:2, amino acid residues X_(4aa) to X_(5aa)of SEQ ID NO:4, amino acid residues X_(4ab) to X_(5ab) of SEQ ID NO:6,amino acid residues X_(4ac) to X_(5ac) of SEQ ID NO:8, and amino acidresidues X_(4ae) to X_(5ae) of SEQ ID NO: 10; and the sixth domain ofamino acid residues is selected from a group consisting of amino acidresidues X_(5b) to X_(6b) of SEQ ID NO:2, amino acid residues X_(5aa) toX_(6aa) of SEQ ID NO:4, amino acid residues X_(5ab) to X_(6ab) of SEQ IDNO:6, amino acid residues X_(5ac) to X_(6ae) of SEQ ID NO:8, and aminoacid residues X_(5ac) to X_(6ae) of SEQ ID NO: 10; wherein X_(1b) is 43,44, 45, 46, 47, 48, 49, 50, 51, or 52; X_(2b) is 61, 62, 63, 64, 65, 66,67, 68, 69, or 70; X_(3b) is 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85,86, 87, or 88; X_(4b) is 95, 96, 97, 98, 99, 100, 101, 102, or 103;X_(5b) is 107, 108, 109, 110, 111, 112, 113, 114, or 115; X_(6b) is 130,131, or 132; X_(1aa) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31;X_(2aa) is 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or 51; X_(3aa) is 55,51, 52, 53.54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,69, 70, 71, 72, 73, or 74; X_(4aa) is 79, 80, 81, 82, 83, 84, 85, 86, or87; X_(5aa) is 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100; X_(6aa) is114, 115, or 116; X_(1ab) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31;X_(2ab) is 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or 51; X_(3ab) is 55,51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,69, 70, 71, 72, 73, or 74; X_(4ab) is 78, 79, 80, 81, 82, 83, 84, 85, or86; X_(5ab) is 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99; X_(6ab) is113, 114, or 115; X_(1ac) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31;X_(2ac) is 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or 51; X_(3ac) is 55,51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,69, 70, 71, 72, 73, or 74; X_(4ac) is 79, 80, 81, 82, 83, 84, 85, 86, or87; X_(5ac) is 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100; X_(6ac) is114, 115, or 116; X_(1ae) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31;X_(2ae) is 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or 51; X_(3ae) is 55,51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,69, 70, 71, 72, 73, or 74; X_(4ae) is 77, 78, 79, 80, 81, 82, 83, 84, or85; X_(5ae) is 89, 90, 91, 92, 93, 94, 95, 96, 97, or 98; and X_(6ae) is112, 113, or 114; and wherein the chimeric polypeptide is capable ofbinding to one or more of Transforming Growth Factor-beta (TGF-β)superfamily members; or one or more of TGF-β receptors.

2. The chimeric polypeptide of as set forth in 1, wherein the sequenceof said polypeptide is described by an algorithm 1n2n3n4n5n6n, whereinsaid 1n, 2n, 3n, 4n, 5n, and 6n represent respectively the first,second, third, fourth, fifth, and sixth domain; and said n is either aor b, and wherein said a represents an amino acid sequence derived fromthe sequence of SEQ ID NO:2; and said b represents an amino acidsequence derived from any one selected from the group consisting of SEQID NO:4, SEQ ID NO:6, SEQ ID NO:8, and SEQ ID NO: 10.

3. The chimeric polypeptide of as set forth in 2, wherein the sequenceof said polypeptide is described by an algorithm 1b2a3b4b5a6a.

4. The chimeric polypeptide of as set forth in 1, wherein said firstdomain comprises amino acid residues 1 to 47 of SEQ ID NO:2; said seconddomain comprises amino acid residues 28 to 45 of SEQ ID NO:4; said thirddomain comprises amino acid residues 66 to 85 of SEQ ID NO:2; saidfourth domain comprises amino acid residues 86 to 99 of SEQ ID NO:2;said fifth domain comprises amino acid residues 84 to 95 of SEQ ID NO:4;and said sixth domain comprises amino acid residues 96 to 116 of SEQ IDNO:4.

5. The chimeric polypeptide of as set forth in 1, wherein saidpolypeptide comprises the sequence as set forth in SEQ ID NO: 12.

6. The chimeric polypeptide of as set forth in 1, wherein saidpolypeptide has at least 95% sequence identity to the sequence as setforth in SEQ ID NO: 12.

7. The chimeric polypeptide of as set forth in 1, wherein said chimericpolypeptide has at least 97% sequence identity to the amino acidsequence comprising said first domain, said second domain, said thirddomain, said fourth domain, said fifth domain, and said sixth domain.

8. A homo-dimer of the chimeric polypeptide of as set forth in 1, 2, 3,4, 5, 6, or 7.

9. A hetero-dimer of the chimeric polypeptide of as set forth in 1, 2,3, 4, 5, 6, or 7.

Advantageous Effects of Invention

The chimeric polypeptide of an embodiment can refold efficiently and canbe produced at a high yield.

The chimeric polypeptide of an embodiment alone or in combination with apharmaceutically acceptable carrier can be used to treat a liverdisease.

The chimeric polypeptide of an embodiment alone or in combination with apharmaceutically acceptable carrier can be used to treat a bone andcartilage disease.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the strategies used in an embodiment for generatingactivin/BMP-6 chimeras, such as AB604, using domains from two differentligands in TGF-beta superfamily.

FIG. 2 shows sequence comparison of TGF-beta superfamily members.

FIG. 3 shows refolding efficiency of BMP-2, 3, 6 and 7.

FIG. 4 shows regions with sequence identity between BMP-6 and Activinwhich were identified as putative cross-over points.

FIG. 5 shows amino acid sequence of AB604.

FIG. 6 shows SDS-PAGE gel of AB604 showing that AB604 exists as monomersin the inclusion bodies.

FIG. 7 shows reducing and non-reducing SDS-PAGE showing that purifiedactivin/BMP-6 chimeras were disulfide-bonded dimers.

FIG. 8 shows comparison of Smad-1 signaling activity of AB604, BMP-2 andBMP-6.

FIG. 9 shows comparison of Smad-1 signaling activity of AB604 and AB204

FIG. 10 shows Smad-2 signaling activity of AB604.

FIG. 11 shows inhibition of signaling activity of TGFβ1 by BMP6.

FIG. 12 shows inhibition of signaling activity of TGFβ1 by BMP6 in thepresence of 3.0 ng/ml of TGFβ1.

FIG. 13 shows inhibition of signaling activity of TGFβ1 by AB604.

FIG. 14 shows inhibition of signaling activity of TGFβ1 by AB604 in thepresence of 3.0 ng/ml of TGFβ1.

FIG. 15 shows suppression of BMP2, BMP6, or AB604 activity by noggin.

FIG. 16 shows comparison of hepcidin expression regulation by BMP6 andAB604.

FIG. 17 shows comparison of dose-dependent profile of hepcidin geneexpression by BMP6 and AB604.

FIG. 18 shows comparison of SMAD1/5/8 phosphorylation by AB604, TGFβ1and BMP6.

FIG. 19 shows comparison of SMAD2 phosphorylation by AB604, TGFβ1 andBMP6.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment provides a non-naturally occurring chimeric polypeptidehaving an activity provided by a TGF-beta family member. The chimericpolypeptide of an embodiment comprises two or more domains or fragmentsfrom parental TGF-beta proteins operably linked such that the resultingpolypeptide is capable of modulating a pathway associated with aTGF-beta family member. In one embodiment, the pathway is a SMAD pathwayor a DAXX (Death-associated protein 6) pathway.

An embodiment of the invention provides designer TGF-beta ligands thatcan be synthesized by selecting and conjoining different domains ofTGF-beta superfamily ligands to construct new ligands (i.e. designerligands). These novel chimeric ligands possess entirely new proteinsequence library that differs from naturally existing TGF-betasuperfamily ligands. This approach originates primarily from therecognition of the structural commonality among natural TGF-betasuperfamily ligands. All ˜40 TGF-beta superfamily ligands share the sameoverall architecture with generic characteristics for each region of theprotein. The framework of TGF-beta ligands can be divided into(generally) six domains that all superfamily members share.

An embodiment of the invention provides a chimeric polypeptidecomprising: at least two domains, a first domain of the polypeptidecomprising a sequence having at least 80% identity to a first TGF-betafamily protein and a second domain comprising a sequence having at least80% identity to a second TGF-beta family protein, wherein the domainsare operably linked and have activity of at least one of the first orsecond parental TGF-beta family protein. In one embodiment, the chimericpolypeptide comprises 6 domains operably linked N-terminus toC-terminus. In one embodiment, each of the first and second TGF-betafamily proteins has structural similarity and each domain corresponds toa structural motif. In one embodiment, the first TGF-beta family proteinis BMP-6 and the second TGF-beta family protein is activin. In oneembodiment, the polypeptide comprises an N-terminal domain from BMP-6.

In one embodiment, the domains of BMP-6, activin-βA, activin-βB,activin-βC, and activin-βE are as described in Table 1, wherein thechimeric polypeptide has an order of domain 1-domain 2-domain 3-domain4-domain 5-domain 6, from the N-terminal to the C-terminal orientation.

An embodiment of the invention provides a chimeric polypeptidecomprising at least 80%, 81%, 82%, 83%, 84%, 85%, 86%, 86%, 87%, 88%,89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more identityto a sequence as set forth in SEQ ID NO: 12 and wherein the polypeptidemodulates the SMAD or DAXX pathway.

An embodiment of the invention provides a chimeric TGF-beta familypolypeptide comprising a domain of a first TGF-beta family proteinoperably linked to a domain of a second different TGF-beta familyprotein to provide a chimeric polypeptide having SMAD or DAXX modulatingactivity. In one embodiment, the chimeric TGF-beta family polypeptidecomprises at least 80%, 81%, 82%, 83%, 84%, 85%, 86%, 86%, 87%, 88%,89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more identityto the sequence as set forth in SEQ ID NO: 12 and wherein thepolypeptide modulates the SMAD or DAXX pathway.

An embodiment of the invention provides a polynucleotide encoding apolypeptide of an embodiment. In one embodiment, the polynucleotide hasat least 80%, 81%, 82%, 83%, 84%, 85%, 86%, 86%, 87%, 88%, 89%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%98%, 99% or more identity to a sequenceas set forth in SEQ ID NO: 11. A vector comprising such polynucleotideis also provided along with a recombinant cell.

An embodiment of the invention provides novel ligands of the TGF-betasuperfamily, wherein each of the ligands is a chimeric protein with atleast one of six domains from a foreign or different member of theTGF-beta superfamily.

As used herein and in the appended claims, the singular forms “a,”“and,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a domain” includesa plurality of such domains and reference to “the protein” includesreference to one or more proteins, and so forth.

Also, the use of “or” means “and/or” unless stated otherwise. Similarly,“comprise,” “comprises,” “comprising” “include,” “includes,” and“including” are interchangeable and not intended to be limiting.

It is to be further understood that where descriptions of variousembodiments use the term “comprising,” those skilled in the art wouldunderstand that in some specific instances, an embodiment can bealternatively described using language “consisting essentially of” or“consisting of.”

Although methods and materials similar or equivalent to those describedherein can be used in the practice of the disclosed methods andcompositions, the exemplary methods and materials are described herein.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this disclosure belongs. Thus, as used throughout theinstant application, the following terms shall have the followingmeanings.

“Amino acid” is a molecule having the structure wherein a central carbonatom (the alpha-carbon atom) is linked to a hydrogen atom, a carboxylicacid group (the carbon atom of which is referred to herein as a“carboxyl carbon atom”), an amino group (the nitrogen atom of which isreferred to herein as an “amino nitrogen atom”), and a side chain group,R. When incorporated into a peptide, polypeptide, or protein, an aminoacid loses one or more atoms of its amino acid carboxylic groups in thedehydration reaction that links one amino acid to another. As a result,when incorporated into a protein, an amino acid is referred to as an“amino acid residue.”

“Protein” or “polypeptide” refers to any polymer of two or moreindividual amino acids (whether or not naturally occurring) linked via apeptide bond, and occurs when the carboxyl carbon atom of the carboxylicacid group bonded to the alpha-carbon of one amino acid (or amino acidresidue) becomes covalently bound to the amino nitrogen atom of aminogroup bonded to the carbon of an adjacent amino acid. The term “protein”is understood to include the terms “polypeptide” and “peptide” (which,at times may be used interchangeably herein) within its meaning. Inaddition, proteins comprising multiple polypeptide subunits (e.g., DNApolymerase ill, RNA polymerase 11) or other components (for example, anRNA molecule, as occurs in telomerase) will also be understood to beincluded within the meaning of “protein” as used herein. Similarly,fragments of proteins and polypeptides are also within the scope of thepresent invention and may be referred to herein as “proteins.” In oneaspect of an embodiment, a polypeptide comprises a chimera of two ormore parental domains.

As used herein, TGF-beta superfamily member refers to a TGF-betasuperfamily (including bone morphogenic factors) gene or protein of anyspecies, particularly a mammalian species, including but not limited tobovine, ovine, porcine, murine, equine, and human. “TGF-beta superfamilypolypeptide” refers to the amino acid sequences of purified TGF-betasuperfamily protein obtained from any species, particularly a mammalianspecies, including bovine, ovine, porcine, murine, equine, and human andfrom any source, whether natural, synthetic, semi-synthetic, orrecombinant.

A particular amino acid sequence of a given protein (i.e., thepolypeptide's “primary structure,” when written from the amino-terminusto carboxy-terminus) is determined by the nucleotide sequence of thecoding portion of a mRNA, which is in turn specified by geneticinformation, typically genomic DNA (including organelle DNA, e.g.,mitochondrial or chloroplast DNA). Thus, determining the sequence of agene assists in predicting the primary sequence of a correspondingpolypeptide and more particular the role or activity of the polypeptideor proteins encoded by that gene or polynucleotide sequence.

“Fused,” “operably linked,” and “operably associated” are usedinterchangeably herein to broadly refer to a chemical or physicalcoupling of two otherwise distinct domains, wherein each domain hasindependent biological function. As such, an embodiment of the inventionprovides TGF-beta (e.g., BMP-6 or activin) domains that are fused to oneanother such that they function as a polypeptide having a TGF-betafamily activity or an improvement or change in ligand specificity of aTGF-beta family of polypeptides. In one embodiment, a chimericpolypeptide comprising a plurality of domains from two parental TGF-betafamily polypeptides are linked such that they are part of the samecoding sequence, each domain encoded by a polynucleotide from a parentalTGF-beta family polypeptide, wherein the polynucleotide is in frame suchthat the polynucleotide when transcribed encodes a single mRNA that whentranslated comprises a plurality of domains as a single polypeptide.Typically, the coding domains will be linked “in-frame” either directlyor separated by a peptide linker and encoded by a single polynucleotide.Various coding sequences for peptide linkers and peptide are known inthe art.

“Polynucleotide” or “nucleic acid” refers to a polymeric form ofnucleotides. In some instances a polynucleotide comprises a sequencethat is not immediately contiguous with either of the coding sequenceswith which it is immediately contiguous (one on the 5′ end and one onthe 3′ end) in the naturally occurring genome of the organism from whichit is derived. The term therefore includes, for example, a recombinantDNA which is incorporated into a vector, into an autonomouslyreplicating plasmid or virus; or into the genomic DNA of a prokaryote oreukaryote, or which exists as a separate molecule (e.g., a cDNA)independent of other sequences. The nucleotides of an embodiment can beribonucleotides, deoxyribonucleotides, or modified forms of eithernucleotide. A polynucleotide as used herein refers to, among others,single- and double-stranded DNA, DNA that is a mixture of single- anddouble-stranded regions, single- and double-stranded RNA, and RNA thatis mixture of single- and double-stranded regions, hybrid moleculescomprising DNA and RNA that may be single-stranded or, more typically,double-stranded or a mixture of single- and double-stranded regions. Theterm polynucleotide encompasses genomic DNA or RNA (depending upon theorganism, i.e., RNA genome of viruses), as well as mRNA encoded by thegenomic DNA, and cDNA.

“Chimera” or “chimeric protein” or “chimeric polypeptide” refers to acombination of at least two domains of at least two different parentproteins. For example, a chimeric BMP will have at least two domainsfrom two different parent BMPs; or BMP and other member of the TGF-betasuperfamily (for example, activins), or alternatively, an unrelatedprotein. A chimeric protein may also be an “interspecies,” “intergenic,”etc. fusion of protein structures (the same or different member protein)expressed by different kinds of organisms. In one embodiment, twodomains are connected so as to result in a new chimeric protein. Inother words, a protein will not be a chimera if it has the identicalsequence of either one of the full-length parents. A chimeric proteincan comprise more than two domains from two different parent proteins.For example, there may be 2, 3, 4, 5, 6 or 10-20, or more parents fromwhich the domains may be derived in generating a final chimera orlibrary of chimeras. The domain of each parent protein can be very shortor very long, the domains can range in length of contiguous amino acidsfrom 1 to about the full length of the protein. In one embodiment, theminimum length is 5 amino acids. Generally, the domain, is one of sixdomains, alternatively five domains (see FIG. 2).

The six domains of a TGF-beta superfamily member are identified based onthe structural architecture of the member protein and/or the primaryamino acid sequence as aligned against other homologous member proteins.As identified, the member protein is generally divided into 6 distinctdomains (although, alternatively, 5 distinct domains) based on domainsderived to minimize alterations, or alternatively viewed, maximizealterations, to the aligned native TGF-beta member sequence duringchimera engineering. Generally, FIG. 2 shows the relative positions ofthe distinct domains overlapping the aligned sequences of each ofseveral TGF-beta superfamily members. The vertical line denotes ageneral position for cross-over between domains in generating thechimera. The amino acids that can overlap the two domains can be definedas being plus or minus about 5 amino acids (or alternatively, 8, 7, 6,5, 4, 3, 2 or 1 amino acids) in either direction of the vertical line.Also in FIG. 2 is shown a boxed set of amino acids that identifyadditional junctions that can be used to generate chimera. The J1-J5junctions are positions general conservation across the TGF-beta familyproteins that can be used to generate cross-over points.

Although relatively distinct, the domains may comprise a particularamino acid sequence or an original amino acid sequence that is amenableto substitution(s), insertion(s), additional amino acid(s) at either orboth termini of the original sequence, or other modifications. By“amenable”, it is meant that the structural integrity of each domain ismaintained as compared to the domain of the original sequence. Forexample, a domain described herein of a TGF-beta superfamily member mayshift by 10, 5, 3, 2, or 1, or preferably no more than 1 amino acid oneither or both termini of domain as identified. An embodiment of theinvention provides a chimeric protein comprising a fusion of at leastone domain from a TGF-beta member with a second domain from a secondTGF-beta member, wherein the first domain is foreign to the secondTGF-beta member. Utilizing the five-six domains on a single subunit ofthe TGF-beta superfamily ligand as a scaffold framework, new (designer)sequences can be recombinantly linked by mixing domains from differentTGF-beta ligands in the same order as they appear in nature. Thisassembly produces new sequences that are partly similar to one ofseveral different target sequences, but distinctly different from anynaturally occurring sequences.

In one embodiment, a single crossover point is defined for the aminoacid sequences of two parents. The crossover location defines where oneparent's domain will stop and where the next parent's domain will start.Thus, a simple chimera would only have one crossover location where thedomain before that crossover location would belong to one parent and thedomain after that crossover location would belong to the second parent.In one embodiment, the chimera has more than one crossover location. Forexample, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11-30, or more crossover locations.In one embodiment, the parental strands are defined as having 1, 2, 3, 4or 5 crossover locations. How these crossover locations are named anddefined are both discussed below. In an embodiment where there are twocrossover locations and two parents, there will be a first contiguousdomain from a first parent, followed by a second contiguous domain froma second parent, followed by a third contiguous domain from the firstparent. Contiguous is meant to denote that there is nothing ofsignificance interrupting the domains. These contiguous domains areconnected to form a contiguous amino acid sequence. For example, anactivin/BMP-6 chimera derived from a BMP-6 wild-type parental strand andan activin wild-type parental strand with five crossovers would comprisea first domain from either BMP-6 or activin, a second domain from theopposite parental strand compared to the first domain operably linked tothe first domain and comprising a structural motif downstream of thefirst domain, a third domain from the opposite parental strand comparedto the second domain operably linked to the second domain and comprisinga structural motif downstream of the second domain, a fourth domain fromthe opposite parental strand compared to the third domain operablylinked to the third domain and comprising a structural motif downstreamof the third domain, a fifth domain from the opposite parental strandcompared to the fourth domain operably linked to the fourth domain andcomprising a structural motif downstream of the fourth domain, and asixth domain from the opposite parental strand compared to the fifthdomain operably linked to the fifth domain and comprising a structuralmotif downstream of the fifth domain, all connected in one contiguousamino acid chain.

As appreciated by one of skill in the art, variants of chimeras exist aswell as the exact sequences. In other words conservative amino acidsubstitutions may be incorporated into the chimera (e.g., from about1-10 conservative amino acid substitutions). Thus, not 100% of eachdomain need be present in the final chimera if it is a variant chimera.The amount that may be altered, either through additional residues orremoval or alteration of residues will be defined as the term variant isdefined. Of course, as understood by one of skill in the art, the abovediscussion applies not only to amino acids but also nucleic acids whichencode for the amino acids.

“Conservative amino acid substitution” refers to the interchangeabilityof residues having similar side chains, and thus typically involvessubstitution of the amino acid in the polypeptide with amino acidswithin the same or similar defined class of amino acids. By way ofexample and not limitation, an amino acid with an aliphatic side chainmay be substituted with another aliphatic amino acid, e.g., alanine,valine, leucine, isoleucine, and methionine; an amino acid with hydroxylside chain is substituted with another amino acid with a hydroxyl sidechain, e.g., serine and threonine; an amino acids having aromatic sidechains is substituted with another amino acid having an aromatic sidechain, e.g., phenylalanine, tyrosine, tryptophan, and histidine; anamino acid with a basic side chain is substituted with another aminoacid with a basis side chain, e.g., lysine, arginine, and histidine; anamino acid with an acidic side chain is substituted with another aminoacid with an acidic side chain, e.g., aspartic acid or glutamic acid;and a hydrophobic or hydrophilic amino acid is replaced with anotherhydrophobic or hydrophilic amino acid, respectively.

“Non-conservative substitution” refers to substitution of an amino acidin the polypeptide with an amino acid with significantly differing sidechain properties. Non-conservative substitutions may use amino acidsbetween, rather than within, the defined groups and affects (a) thestructure of the peptide backbone in the area of the substitution (e.g.,proline for glycine) (b) the charge or hydrophobicity, or (c) the bulkof the side chain. By way of example and not limitation, an exemplarynon-conservative substitution can be an acidic amino acid substitutedwith a basic or aliphatic amino acid; an aromatic amino acid substitutedwith a small amino acid; and a hydrophilic amino acid substituted with ahydrophobic amino acid.

“Reference sequence” refers to a defined sequence used as a basis for asequence comparison. A reference sequence may be a subset of a largersequence, for example, a domain of a full-length gene or polypeptidesequence. Generally, a reference sequence can be at least 20 nucleotideor amino acid residues in length, at least 25 residues in length, atleast 50 residues in length, or the full length of the nucleic acid orpolypeptide. Since two polynucleotides or polypeptides may each (1)comprise a sequence (i.e., a portion of the complete sequence) that issimilar between the two sequences, and (2) may further comprise asequence that is divergent between the two sequences, sequencecomparisons between two (or more) polynucleotides or polypeptides aretypically performed by comparing sequences of the two polynucleotides orpolypeptides over a “comparison window” to identify and compare localregions of sequence similarity.

“Sequence identity” means that two amino acid sequences aresubstantially identical (i.e., on an amino acid-by-amino acid basis)over a window of comparison. The term “sequence similarity” refers tosimilar amino acids that share the same biophysical characteristics. Theterm “percentage of sequence identity” or “percentage of sequencesimilarity” is calculated by comparing two optimally aligned sequencesover the window of comparison, determining the number of positions atwhich the identical residues (or similar residues) occur in bothpolypeptide sequences to yield the number of matched positions, dividingthe number of matched positions by the total number of positions in thewindow of comparison (i.e., the window size), and multiplying the resultby 100 to yield the percentage of sequence identity (or percentage ofsequence similarity). With regard to polynucleotide sequences, the termssequence identity and sequence similarity have comparable meaning asdescribed for protein sequences, with the term “percentage of sequenceidentity” indicating that two polynucleotide sequences are identical (ona nucleotide-by-nucleotide basis) over a window of comparison. As such,a percentage of polynucleotide sequence identity (or percentage ofpolynucleotide sequence similarity, e.g., for silent substitutions orother substitutions, based upon the analysis algorithm) also can becalculated. Maximum correspondence can be determined by using one of thesequence algorithms described herein (or other algorithms available tothose of ordinary skill in the art) or by visual inspection.

As applied to polypeptides, the term substantial identity or substantialsimilarity means that two peptide sequences, when optimally aligned,such as by the programs BLAST, GAP or BESTFIT using default gap weightsor by visual inspection, share sequence identity or sequence similarity.Similarly, as applied in the context of two nucleic acids, the termsubstantial identity or substantial similarity means that the twonucleic acid sequences, when optimally aligned, such as by the programsBLAST, GAP or BESTFIT using default gap weights (described in detailbelow) or by visual inspection, share sequence identity or sequencesimilarity.

One example of an algorithm that is suitable for determining percentsequence identity or sequence similarity is the FASTA algorithm, whichis described in Pearson, W. R. & Lipman, D. J., (1988) Proc. Natl. Acad.Sci. USA 85:2444. See also, W. R. Pearson, (1996) Methods Enzymology266:227-258. Preferred parameters used in a FASTA alignment of DNAsequences to calculate percent identity or percent similarity areoptimized, BL50 Matrix 15: 5, k-tuple=2; joining penalty=40,optimization=28; gap penalty 12, gap length penalty=2; and width=16.

Another example of a useful algorithm is PILEUP. PILEUP creates amultiple sequence alignment from a group of related sequences usingprogressive, pairwise alignments to show relationship and percentsequence identity or percent sequence similarity. It also plots a treeor dendogram showing the clustering relationships used to create thealignment. PILEUP uses a simplification of the progressive alignmentmethod of Feng & Doolittle, (1987) J. Mol. Evol. 35:351-360. The methodused is similar to the method described by Higgins & Sharp, CABIOS5:151-153, 1989. The program can align up to 300 sequences, each of amaximum length of 5,000 nucleotides or amino acids. The multiplealignment procedure begins with the pairwise alignment of the two mostsimilar sequences, producing a cluster of two aligned sequences. Thiscluster is then aligned to the next most related sequence or cluster ofaligned sequences. Two clusters of sequences are aligned by a simpleextension of the pairwise alignment of two individual sequences. Thefinal alignment is achieved by a series of progressive, pairwisealignments. The program is nm by designating specific sequences andtheir amino acid or nucleotide coordinates for regions of sequencecomparison and by designating the program parameters. Using PILEUP, areference sequence is compared to other test sequences to determine thepercent sequence identity (or percent sequence similarity) relationshipusing the following parameters: default gap weight (3.00), default gaplength weight (0.10), and weighted end gaps. PILEUP can be obtained fromthe GCG sequence analysis software package, e.g., version 7.0 (Devereauxet al., (1984) Nuc. Acids Res. 12:387-395).

Another example of an algorithm that is suitable for multiple DNA andamino acid sequence alignments is the CLUSTALW program (Thompson, J. D.et al., (1994) Nuc. Acids Res. 22:4673-4680). CLUSTALW performs multiplepairwise comparisons between groups of sequences and assembles them intoa multiple alignment based on sequence identity. Gap open and Gapextension penalties were 10 and 0.05 respectively. For amino acidalignments, the BLOSUM algorithm can be used as a protein weight matrix(Henikoff and Henikoff, (1992) Proc. Natl. Acad. Sci. USA89:10915-10919).

FIG. 2, for example, shows an alignment of a number of TGF-beta familymembers. One of skill in the art can readily determine from thealignment those amino acids that are conserved across the family as wellas those that are not conserved.

“Functional” refers to a polypeptide which possesses either the nativebiological activity of the naturally-produced proteins of its type, orany specific desired activity, for example as judged by its ability tobind to ligand or cognate molecules or induce a particular biologicalfunction (e.g., stimulate muscle growth, bone growth and the like).

The Transforming Growth Factor-beta (TGF-β) superfamily of proteins iscomprised of extracellular cytokines found in the vast majority of humancells. The TGF-β superfamily ligands, of which there are ˜40, can besubdivided into smaller families including TGF-β. Bone MorphogeneticProteins (BMPs), activin and inhibin, Growth and Differentiation Factors(GDFs), Nodal, Mullerian Inhibiting Substance (MIS), and Glial cellline-Derived Neurotrophic Factors (GDNFs). TGF-β superfamily members arefound in a diverse range of cell types and play roles in manyfundamental cellular events including dorsal/ventral patterning andleft/right axis determination to bone formation and tissue repair. Morerecently, several TGF-β ligands have been shown to be involved in themaintenance or direct the differentiation of stem cells. Due to theirpervasiveness, regulation of TGF-β ligand signaling holds promise forthe treatment of a wide range of different diseases from skeletal andmuscle abnormalities to numerous neoplastic events. Exemplary sequencesare provided herein for various members of this family or proteins,however, one of skill in the art can easily identify homologs andvariants using publicly available databases by word search or sequenceBLAST searches.

There are generally recognized several subfamilies within thesuperfamily of TGF-beta (TGF-β1-β5) as well as the differentiationfactors (e.g., Vg-1), the hormones activin and inhibin, the Mullerianinhibiting substance (MIS), osteogenic and morphogenic proteins (e.g.,OP-1, OP-2, OP-3, other BMPs), the developmentally regulated proteinVgr-1, the growth/differentiation factors (e.g., GDF-1, GDF-3, GDF-9 anddorsalin-1), etc. See, e.g., Spam and Roberts (1990) in Peptide GrowthFactors and Their Receptors, Spom and Roberts, eds., Springer-Verlag:Berlin pp. 419-472; Weeks and Melton (1987) Cell 51: 861-867; Padgett etal. (1987) Nature 325: 81-84; Mason et al. (1985) Nature 318: 659-663;Mason et al. (1987) Growth Factors 1: 77-88; Cate et al. (1986) Cell 45:685-698; PCT/US90/05903; PCT/US91/07654; PCT/WO94/10202; U.S. Pat. Nos.4,877,864; 5,141,905; 5,013,649; 5,116,738; 5,108,922; 5,106,748; and5,155,058; Lyons et al. (1989) Proc. Natl. Acad. Sci. USA 86: 4554-58;McPherron et al. (1993) J. Biol. Chem. 268: 3444-3449; Easier et al.(1993) Cell 73: 687-702.

Morphogenic proteins of the TGF-beta superfamily include the mammalianosteogenic protein-1 (OP-1, also known as BMP-7), osteogenic protein-2(OP-2, also known as BMP-8), osteogenic protein-3 (053). BMP-2 (alsoknown as BMP-2A or CBMP-2A, and the Drosophila homolog DPP), BMP-3,BMP-4 (also known as BMP26 or CBMP-2B). BMP-5, BMP-6 and its murinehomolog Vgr-1, BMP-9, BMP-10, BMP-11, BMP-12, GDF3 (also known as Vgr2),GDF-8, GDF-9, GDF-10. GDF-11, GDF-12, BMP-13, BMP-14, BMP-15, GDF-5(also known as CDMP-1 or MP52), GDF-6 (also known as CDMP-2 or BMP13),GDF-7 (also known as CDMP-3 or BMP-12), the Xenopus homolog Vg1 andNODAL, UNIVIN, SCREW, ADMP, NEURAL, etc.

TGF-β ligands are synthesized as inactive precursor molecules composedof an N-terminal pro-domain and a C-terminal mature domain linked by aprotease cleavage site. To be become active, the mature domain must becleaved from the pro-domain, commonly by a convertase, such as furin.Members of the TGF-β superfamily are classified together due to theconserved structural architecture found in their mature domains. Ingeneral, each mature ligand monomer contains 7 cysteines, 6 of whichform three intra-disulfide bonds arranged in a ‘cysteine knot’ motif.Stretching outward from the ‘cysteine knot’ are 4 beta strands, creating2 curved fingers. The last remaining cysteine forms an inter-disulfidebond with a second ligand monomer, generating a covalently linked dimer.The dimer has the overall appearance of a butterfly with the ‘cysteineknot’ as the body and the fingers spreading out like wings. Thefunctional subunit for the TGF-β superfamily is the dimer and they beenshown to exist both as homo- and heterodimers in vivo. Some familymembers, such as GDF-9 and BMP-15, lack the cysteine required to formthe inter-disulfide bond yet they are still able to form stable dimers.

To initiate the signaling process, TGF-β dimers must recruit two sets ofreceptors, termed type I and type II. These receptors areserine/threonine kinases possessing an extracellular domain (ECD)ordered into a three-finger toxin fold, a single transmembrane domain,and a large intracellular kinase domain. TGF-β ligands have been shownto display preferences in their affinity for the different receptortypes. Activin and Nodal exhibit high affinity for type 11 receptors,while BMP-2 and GDF-5 possess higher affinity for type 1 receptors.Following the binding of two high affinity receptors to a TGF-β ligand,two lower affinity receptors are then able to bind and join the complex.Upon binding of all four receptors to the TGF-β ligand, forming a6-member ternary complex, the downstream signaling cascade is initialed.The constitutively active type II receptors phosphorylate the type Ireceptors which, in turn, bind and phosphorylate intracellular signalingmolecules called Smads. The Smad molecules then are able to translocateto the nucleus and interact directly with transcriptional regulators.Multiple mechanisms are employed to closely regulate TGF-β signaling atdifferent stages of the cascade: Extracellular antagonists, includingNoggin, follistatin, and Inhibin; pseudo-receptors lacking theintracellular kinase domain, similar to BAMBI; or through intracellularmolecules, such as inhibitory Smads.

TGF-β superfamily shows a high degree of promiscuity by receptors forthe ligands. While there are over 40 TGF-β ligands, there are only 12receptors (7 type I and 5 type II). Therefore, receptors must be able tointeract with a multitude of different ligands. For instance, ActRII isknown to bind activin and BMP-7 with high affinity, but binds BMP-2 withmuch lower affinity. In GDF-5, a single amino acid has been found whichdetermines its type I receptor preference, while in BMP-3 a single pointmutation was discovered which alters type II receptor affinity as wellas imparting function to the ligand. An embodiment provides methods tocreate modified TGF-β ligands with novel receptor binding propertiesthereby diversifying TGF-β ligand function as well as a compositionhaving such activity.

An embodiment demonstrates a TGF-beta signaling complex by utilizingnovel ligand constructs. Using synthesized chimeric homo- orheterodimeric ligands, an embodiment provides a composition for use indissecting the signaling of TGF-beta family proteins. Furthermore,utilizing such ligands allows a method for distinguishing contributionsof two type I receptor interfaces from each other, and two type IIreceptor interfaced each other. The methods and compositions of anembodiment demonstrate a correlation between ligand-receptor affinity,signaling activity, and biological activity. The methods andcompositions of an embodiment shed light on the mechanism andrequirements of the TGF-beta superfamily signaling complex assembly. Inaddition the chimeric ligands provide novel polypeptides for use intreating diseases and disorders associated with TGF-β family ofproteins.

An embodiment provides methods of making and using a novel chimericTGF-β ligand which possesses the ability to be expressed and refoldedusing, for example, an E. coli or mammalian expression system. Thestrategies used in an embodiment for generating an activin/BMP-6chimera, such as AB604, using domains from two different ligands inTGF-beta superfamily are summarized in FIG. 1. The chimera either mimica specific TGF-β ligand's signaling characteristics or display uniquesignaling properties not seen in nature. In one embodiment, activin-βAand BMP-6 are used as templates to generate an activin/BMP-6 chimera.The activin/BMP-6 chimera of an embodiment shows 7-fold increase inSmad-1 signaling activity and 10-fold increase in refolding yield,compared to activin/BMP-2 (AB204). These superior properties of theactivin/BMP-6 chimera of an embodiment could not have been anticipatedbefore, considering that BMP-2 was believed to have the highestrefolding efficiency among BMP proteins and that BMP-2 was also believedto show higher Smad-1 signaling activity compared to BMP-6, as describedin Allendorph et al. Biochemistry, 2007:12238-47 (FIG. 3).

In one embodiment, two factors were considered when looking to designthe domains of the chimera. First was a structural consideration. Theoverall TGF-β monomer fold is divided into 6 domains naturally: Betastrand 1 and 2, the pre-helix loop, alpha helix 1, and beta strand 3 and4. The identification and characterization of these domains are furtherdescribed in Example 4. An embodiment utilized chimeric structures tomimic these natural regions in the design. Thus, each domain can beindicated by 1, 2, 3, 4, 5, and 6. The second consideration was tominimize alterations to the aligned native TGF-beta member sequenceduring chimera engineering. Therefore, those regions with sequenceidentity between the 2 protein sequences were identified as putativecross-over points. These regions are suitable for the overlaps in DNAsequence for PCR strategy and will minimize any changes to the naturalsequences. FIG. 4 illustrates the sequence and structure of theseconsiderations. The regions are boxed and numbered according to theirdomain and are mapped onto the ligand monomer. Residue numbering in oneembodiment is based on BMP-6 (SEQ ID NO:2). Thus, cross-over points ingenerating a chimeric polypeptide of an embodiment can be identified byidentifying similar structural motifs in combination with at least 60%,70%, 80%, 90%, 95%, 98%, 99% or 100% identity in a domain of thesequence between changes in the structural motif. Cross-overs at theseregions (which may be between 3 to 20 amino acids) minimize disruptionof the resulting chimeric polypeptide providing a stabilized chimera.

For example, a chimeric polypeptide comprising the algorithm1b2a3b4b5a6a indicates 6 domains, the letter indicating the parentalstrand of each domain. Thus, in the example “1b2a3b4b5a6a”, domain 1 isfrom parental strand “b” for BMP-6, domain 2 is from parental strand “a”for activin, domain 3 is from parental strand “b” for BMP-6, domain 4 isfrom parental strand “b” for BMP-6, domain 5 is from parental strand “a”for activin, and domain 6 is from parental strand “a” for activin.

In one embodiment, crossover between domains of BMP-6 and a secondTGF-beta family protein can occur where structural similarity andsequence similarly overlap. FIG. 4 depicts such an overlap between BMP-6and activin, wherein crossovers can be generated between about residueD42-P52, G62-S65; T82-H85; K94-T100; and S106-D112 (residue numbering isbased on BMP-6 (SEQ ID NO:2)). Sequence alignment of BMP-6 andactivin-βA highlight the boundaries of domains 1 through 6. Activin hasthe extra disulfide bond formed between two Cys.

Other methods for identifying crossover locations may be employed in thegeneration of the chimeric TGF-beta family polypeptide. For example,SCHEMA is a computational based method for predicting which fragments ofhomologous proteins can be recombined without affecting the structuralintegrity of the protein (see, e.g., Meyer et al., (2003) Protein Sci.,12:1686-1693). A chimera with higher stability are identifiable bydetermining the additive contribution of each domain to the overallstability, either by use of linear regression of sequence-stabilitydata, or by reliance on consensus analysis of the MSAs of folded versusunfolded proteins. SCHEMA recombination ensures that the chimera retainbiological function and exhibit high sequence diversity by conservingimportant functional residues while exchanging tolerant ones.

As presented in an embodiment, it has been found that when theserecombined, functional chimeric TGF-beta family polypeptides aregenerated their ligand specificity can be improved or biologicalactivity can be altered or improved compared to an unrecombined parentalpolypeptide. Because of differences in activity/ligand profiles, theseengineered chimeric TGF-beta family polypeptides provide a unique basisto screen for activities for ligand specific activation and inhibition,provide novel therapeutic polypeptides and research reagents.

For example, in the chimera of an embodiment, domains 1, 2, 3, 4, 5, and6 can be selected from the following sequences (TABLE 1) wherein thepolypeptide comprises a structure (domain 1-domain 2-domain 3-domain4-domain 5-domain 6):

TABLE 1 Parental Amino acids SEQ ID (Domain #) NO: Variable definition1-X_(1b) (1) 2 X_(1b) is 43, 44, 45, 46, 47, 48, 49, 50, 51, or 521-X_(1aa) (1) 4 X_(1aa) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 311-X_(1ab) (1) 6 X_(1ab) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 311-X_(1ac) (1) 8 X_(1ac) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 311-X_(1ae) (1) 10 X_(1ae) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31X_(1b)-X_(2b) (2) 2 X_(1b) is 43, 44, 45, 46, 47, 48, 49, 50, 51, or52X_(2b) is 61, 62, 63, 64, 65, 66, 67, 68, 69, or 70 X_(1aa)-X_(2aa)(2) 4 X_(1aa) is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31X_(2aa) is 41,42, 43, 44, 45, 46, 47, 48, 49, 50, or 51 X_(1ab)-X_(2ab) (2) 6 X_(1ab)is 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31X_(2ab) is 41, 42, 43, 44,45, 46, 47, 48, 49, 50, or 51 X_(1ac)-X_(2ac) (2) 8 X_(1ac) is 22, 23,24, 25, 26, 27, 28, 29, 30, or 31X_(2ac) is 41, 42, 43, 44, 45, 46, 47,48, 49, 50, or 51 X_(1ae)-X_(2ae) (2) 10 X_(1ae) is 22, 23, 24, 25, 26,27, 28, 29, 30, or 31 X_(2ae) is 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,or 51 X_(2b)-X_(3b) (3) 2 X_(2b) is 61, 62, 63, 64, 65, 66, 67, 68, 69,or 70X_(3b) is 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, or 88X_(2aa)-X_(3aa) (3) 4 X_(2aa) is 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,or 51X_(3aa) is 55, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,64, 65, 66, 67, 68, 69, 70, 71, 72, 73, or 74 X_(2ab)-X_(3ab) (3) 6X_(2ab) is 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or 51X_(3ab) is 55,51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68,69, 70, 71, 72, 73, or 74 X_(2ac)-X_(3ac) (3) 8 X_(2ac) is 41, 42, 43,44, 45, 46, 47, 48, 49, 50, or 51X_(3ac) is 55, 51, 52, 53, 54, 55, 56,57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, or74 X_(2ae)-X_(3ae) (3) 10 X_(2ae) is 41, 42, 43, 44, 45, 46, 47, 48, 49,50, or 51X_(3ae) is 55, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62,63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, or 74 X_(3b)-X_(4b) (4) 2X_(3b) is 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, or88X_(4b) is 95, 96, 97, 98, 99, 100, 101, 102, or 103 X_(3aa)-X_(4aa)(4) 4 X_(3aa) is 55, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,64, 65, 66, 67, 68, 69, 70, 71, 72, 73, or 74X_(4aa) is 79, 80, 81, 82,83, 84, 85, 86, or 87 X_(3ab)-X_(4ab) (4) 6 X_(3ab) is 55, 51, 52, 53,54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71,72, 73, or 74X_(4ab) is 78, 79, 80, 81, 82, 83, 84, 85, or 86X_(3ac)-X_(4ac) (4) 8 X_(3ac) is 55, 51, 52, 53, 54, 55, 56, 57, 58, 59,60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, or 74X_(4ac) is79, 80, 81, 82, 83, 84, 85, 86, or 87 X_(3ae)-X_(4ae) (4) 10 X_(3ae) is55, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,68, 69, 70, 71, 72, 73, or 74X_(4ae) is 77, 78, 79, 80, 81, 82, 83, 84,or 85 X_(4b)-X_(5b) (5) 2 X_(4b) is 95, 96, 97, 98, 99, 100, 101, 102,or 103X_(5b) is 107, 108, 109, 110, 111, 112, 113, 114, or 115X_(4aa)-X_(5aa) (5) 4 X_(4aa) is 79, 80, 81, 82, 83, 84, 85, 86, or87X_(5aa) is 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 X_(4ab)-X_(5ab)(5) 6 X_(4ab) is 78, 79, 80, 81, 82, 83, 84, 85, or 86X_(5ab) is 90, 91,92, 93, 94, 95, 96, 97, 98, or 99 X_(4ac)-X_(5ac) (5) 8 X_(4ac) is 79,80, 81, 82, 83, 84, 85, 86, or 87X_(5ac) is 91, 92, 93, 94, 95, 96, 97,98, 99, or 100 X_(4ae)-X_(5ae) (5) 10 X_(4ae) is 77, 78, 79, 80, 81, 82,83, 84, or 85X_(5ae) is 89, 90, 91, 92, 93, 94, 95, 96, 97, or 98X_(5b)-X_(6b) (6) 2 X_(5b) is 107, 108, 109, 110, 111, 112, 113, 114, or115X_(6b) is 130, 131, or 132 X_(5aa)-X_(6aa) (6) 4 X_(5aa) is 91, 92,93, 94, 95, 96, 97, 98, 99, or 100X_(6aa) is 114, 115, or 116

In some embodiments, domain 3 may be derived from the same parent aseither domain 2, domain 4 or both domain 2 and 4.

As summarized in FIG. 2, in some embodiments, J1 (Junction 1) betweendomain 1 and domain 2 comprises the consensus sequence Z₁Z₂W, wherein Z₁is selected from the group L, V, F, and M, and Z₂ is G or K, wherein 2of the 3 amino acids are found at the C-terminus of the first domain orthe N-terminus of the second domain. In some embodiment, J2 (Junction 2)between domain 2 and domain 3 comprises the consensus sequence CZ₁G,wherein Z₁, is selected from the group H, S, A, L, I, E, K, Q and D,wherein 2 of the 3 amino acids are found at the C-terminus of the seconddomain or the N-terminus of the third domain. In some embodiment, J3(Junction 3) between domain 3 and domain 4 comprises the consensussequence Z₁Z₂Z₃, wherein Z₁ is selected from the group T, S, P, G and I,Z₂ is selected from the group consisting of N, K, V, M, H and Y, and Z₃is selected from the group consisting of H, Y, S, T and P, wherein 2 ofthe 3 amino acids are found at the C-terminus of the third domain or theN-terminus of the fourth domain. In some embodiment, J4 (Junction 4)between domain 4 and domain 5 comprises the consensus sequence Z₁CZ₂,wherein Z₁ is selected from the group C, S and V, and Z₂ is selectedfrom the group consisting of V, A, I and T, wherein 2 of the 3 aminoacids are found at the C-terminus of the fourth domain or the N-terminusof the Fifth domain. In some embodiment, J5 (Junction 1) between thedomain 5 and domain 6 comprises the consensus sequence Z₁Z₂Z₃, whereinZ₁ is selected from the group L, R and V, Z₂ is selected from the groupconsisting of T, Q, Y, F and M, and Z₃ is selected from the groupconsisting of L, F, Y, K, I, Q, V and T, wherein 2 of the 3 amino acidsare found at the C-terminus of the fifth domain or the N-terminus of thesixth domain.

An embodiment of the invention provides the following domains (Table 2)for each of the TGF-beta family members that may be recombined to form achimera of an embodiment having increased or improved biologicalactivity (e.g., resistance to inactivation and the like).

TABLE 2 Domain Domain Domain Domain Domain Domain 1 2 3 4 5 6 BMP-6 1-4748-65 66-85 86-99 100-111 112-132  (SEQ ID NO: 2) activin-βA 1-27 28-4546-68 69-83 84-95 96-116 (SEQ ID NO: 4) activin-βB 1-27 28-45 46-6869-82 83-94 95-115 (SEQ ID NO: 6) activin-βC 1-27 28-45 46-68 69-8384-95 96-116 (SEQ ID NO: 8) activin-βE 1-27 28-45 46-68 69-81 82-9394-114 (SEQ ID NO: 10)

Thus, as illustrated by various embodiments herein, an embodimentprovides a chimeric TGF-beta family polypeptide, wherein a firstTGF-beta family protein (i.e., a first parental protein), which is BMP-6(SEQ ID NO:2), is recombined with a second different TGF-beta familyprotein (i.e., a second parental protein), which is activin, to providea chimeric polypeptide. (SEQ ID NO:1 shows DNA sequence of BMP-6 DNA.)

In some embodiments, a chimeric polypeptide comprises one or moredomains of a BMP-6 protein, wherein the domains of BMP-6 are asdescribed in Table 1, such that a contiguous polypeptide comprisingdomains 1b2b3b4b5b6b comprises a wild-type BMP-6 following a Methionineresidue resulting from the translation initiation codon (ATG). Homologsand proteins having at least about 80%, 81%, 82%, 83%, 84%, 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, and 99%identity to the foregoing sequences are also included by the presentinvention.

In some embodiments, a chimeric polypeptide comprises one or moredomains of activin proteins, wherein the domains of activin-βA (SEQ IDNO:4), activin-βB (SEQ ID NO:6), activin-βC (SEQ ID NO:8), andactivin-βE (SEQ ID NO:10) are as described in Table 1, such that acontiguous polypeptide comprising domains 1a2a3a4a5a6a comprises awild-type mature activin-βA, activin-βB, activin-βC, or activin-βEprotein or a chimera of activin-βA, activin-βB, activin-βC, andactivin-βE. Homologs and proteins having at least about 80%, 81%, 82%,83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, and 99% identity to the foregoing sequences are also includedby the present invention. (SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7, andSEQ ID NO:9 show DNA sequences of activin-βA, activin-βB, activin-βC,and activin-βE, respectively.)

In other embodiment, the chimeric polypeptide may be fused to anadditional heterologous polypeptide to generate a chimeric fusionpolypeptide. The heterologous polypeptide may be, for example, a peptideuseful for purification or that permits oligomerization of multiplechimeric polypeptides of an embodiment of the present invention. Theheterologous may be chemically conjugated to the chimeric polypeptide ormay be operably linked in-frame with a coding sequence for the chimericpolypeptide.

In one embodiment, the amino acid sequence of the chimeric polypeptideis described by an algorithm 1n2n3n4n5n6n, wherein said 1n, 2n, 3n, 4n,5n, and 6n represent respectively the first, second, third, fourth,fifth, and sixth domain; and said n is either a or b, and wherein said arepresents an amino acid sequence derived from the sequence of SEQ IDNO:2; and said b represents an amino acid sequence derived from any oneselected from the group consisting of SEQ ID NO:4, SEQ ID NO:6, SEQ IDNO:8, and SEQ ID NO: 10. For example, the chimeric polypeptide maycomprise a sequence described by an algorithm selected from the groupconsisting of 1a2b3b4b5b6b; 1a2b3b4b5b6a; 1a2b3b4b5a6a; 1a2b3b4b5a6b;1a2b3b4a5a6a; 1a2b3b4a5b6b; 1a2b3b4a5a6b; 1a2b3b4a5b6a; 1a2b3a4a5a6a;1a2b3a4a5a6b; 1a2b3a4a5b6b; 1a2b3a4a5b6a; 1a2b3a4b5b6b; 1a2b3a4b5b6a;1a2b3a4b5a6a; 1a2b3a4b5a6b; 1a2a3a4a5a6a; 1a2a3a4a5a6b; 1a2a3a4a5b6b;1a2a3a4a5b6a; 1a2a3a4b5b6b; 1a2a3a4b5b6a; 1a2a3a4b5a6b; 1a2a3a4b5a6a;1a2a3b4b5b6b; 1a2a3b4b5b6a; 1a2a3b4b5a6a; 1a2a3b4b5a6b; 1a2a3b4a5a6a;1a2a3b4a5b6a; 1a2a3b4a5b6b; 1a2a3b4a5a6b; 1b2b3b4b5b6b; 1b2b3b4b5b6a;1b2b3b4b5a6a; 1b2b3b4b5a6b; 1b2b3b4a5a6a; 1b2b3b4a5b6b; 1b2b3b4a5a6b;1b2b3b4a5b6a; 1b2b3a4a5a6a; 1b2b3a4a5a6b; 1b2b3a4a5b6b; 1b2b3a4a5b6a;1b2b3a4b5b6b; 1b2b3a4b5b6a; 1b2b3a4b5a6a; 1b2b3a4b5a6b; 1b2a3a4a5a6a;1b2a3a4a5a6b; 1b2a3a4a5b6b; 1b2a3a4a5b6a; 1b2a3a4b5b6b; 1b2a3a4b5b6a;1b2a3a4b5a6b; 1b2a3a4b5a6a; 1b2a3b4b5b6b; 1b2a3b4b5b6a; 1b2a3b4b5a6a;1b2a3b4b5a6b; 1b2a3b4a5a6a; 1b2a3b4a5b6a; 1b2a3b4a5b6b; 1b2a3b4a5a6b,wherein said 1b, 2b, 3b, 4b, 5b, and 6b are respectively said first,second, third, fourth, fifth, and sixth segment of SEQ ID NO:2 and said1a, 2a, 3a, 4a, 5a, and 6a are respectively said first, second, third,fourth, fifth, and sixth segment of any one selected from the groupconsisting of SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8, and SEQ ID NO: 10.

In one embodiment, the amino acid sequence of the chimeric polypeptideis described by an algorithm 1b2a3b4b5a6a.

In one embodiment, said first domain comprises amino acid residues 1 to47 of SEQ ID NO:2; said second domain comprises amino acid residues 28to 45 of SEQ ID NO:4; said third domain comprises amino acid residues 66to 85 of SEQ ID NO:2; said fourth domain comprises amino acid residues86 to 99 of SEQ ID NO:2; said fifth domain comprises amino acid residues84 to 95 of SEQ ID NO:4; and said sixth domain comprises amino acidresidues 96 to 116 of SEQ ID NO:4.

In one embodiment, the amino acid sequence of the chimeric polypeptidecomprises the sequence as set forth in SEQ ID NO: 12.

In one embodiment, the chimeric polypeptide has at least 95% sequenceidentity to the sequence as set forth in SEQ ID NO: 12.

In one embodiment, the chimeric polypeptide has at least 97% sequenceidentity to the amino acid sequence comprising said first domain, saidsecond domain, said third domain, said fourth domain, said fifth domain,and said sixth domain.

In one embodiment, the chimeric polypeptide can form a homo-dimer.

In one embodiment, the chimeric polypeptide can form a hetero-dimer.

In some embodiments, one or more of the domains of a chimericpolypeptide is 100% identical to the parental strand from which eachdomain was derived. In other embodiments one or more of the domains cancomprise an amino acid sequence that has at least 60%, 70%, 80%, 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% or more identity to acorresponding domain in a parental strand. For example, one of more ofthe domains may have one or more conservative amino acid substitutions(e.g., 1-5 conservative amino acid substitutions).

In some embodiments, the chimeric TGF-beta family polypeptide may haveimproved activity compared to one or more of the parental strands fromwhich the chimeric polypeptide is generated. Biological activity of achimeric polypeptide of an embodiment can be measured using any numberof recognized assays in the art for TGF-beta activity. Such assaysinclude, but are not limited to, BIAcore (Surface Plasmon Resonance);C₂Cl₂ luciferase assay: Smad 1/5 reporter system; HEK293 luciferaseassay: Smad 2/3 reporter system; FSH (Follicle Stimulating Hormone)release assay: in rat pituitary cells; BRE (BMP Response Element)luciferase assay: Smad 1/5 reporter HEK 293 cells; Cripto binding assay:Luciferase response measured in presence/absence of Crptio; Human StemCell assay: Maintenance or Differentiation of H9 cells; NMR bindingStudies; Micro mass culture: Bone formation measured in Chick embryos;X-ray Crystallography: Determine Structure of ligand:receptor complexes;Native Gel: Visualization of ligand:receptor complexes; Size ExclusionChromatography (SEC); Visualization of ligand:receptor complexes;Velocity Scan Ultracentrifugation: Visualize ligand:receptor complexformation; and Seldi mass Spectrometry: Accurately determine size ofligands.

The chimeric TGF-beta family polypeptide described herein may beprepared in various forms, such as lysates, crude extracts, or isolatedpreparations.

In some embodiments, the isolated chimeric polypeptide is asubstantially pure polypeptide composition. A “substantially purepolypeptide” refers to a composition in which the polypeptide species isthe predominant species present (i.e., on a molar or weight basis it ismore, abundant than any other individual macromolecular species in thecomposition), and is generally a substantially purified composition whenthe object species comprises at least about 50 percent of themacromolecular species present by mole or % weight. Generally, asubstantially pure polypeptide composition will comprise about 60% ormore, about 70% or more, about 80% or more, about 90% or more, about 95%or more, and about 98% or more of all macromolecular species by mole or% weight present in the composition. In some embodiments, the objectspecies is purified to essential homogeneity (i.e., contaminant speciescannot be detected in the composition by conventional detection methods)wherein the composition consists essentially of a single macromolecularspecies. Solvent species, small molecules (<500 Daltons), and elementalion species are not considered macromolecular species.

An embodiment contemplates making functional variants by modifying thestructure of the chimera. Such modifications may be made, for example,for such purposes as enhancing therapeutic efficacy, or stability (e.g.,ex vivo shelf life and resistance to proteolytic degradation in vivo,improve stability, solubility, bioavailability, or biodistribution ofthe chimeric protein, etc.). For example, but not by way of limitation,the derivatives include a chimera that has been modified, e.g., byacetylation, carboxylation, acylation glycosylation, pegylation,phosphorylation, farnesylation, biotinylation, lipidation, amidation,derivatization by known protecting/blocking groups, proteolyticcleavage, linkage to a cellular ligand or other protein such as anorganic deriatizing agent, etc. Any of numerous chemical modificationsmay be carried out by known techniques, including, but not limited tospecific chemical cleavage, acetylation, formylation, metabolicsynthesis, etc. Additionally, the derivative may contain one or morenon-natural amino acids, such as those with ketone-containing sidechain, polyethylene glycols, lipids, poly- or monosaccharide, andphosphates. Effects of such non-natural amino acid elements on thefunctionality of a chimeric TGF-beta superfamily protein may be testedas described herein for other TGF-beta superfamily protein variants.When a chimeric TGF-beta superfamily protein is produced in cells bycleaving a nascent form of the precursor protein, post-translationalprocessing may also be important for correct folding and/or function ofthe protein. Different cells (such as CHO, HeLa, MDCK, 293, W138,NIH-3T3 or HEK293) have specific cellular machinery and characteristicmechanisms for such post-translational activities and may be chosen toensure the correct post-translational modification and processing of theprecursor protein into a chimeric TGF-beta superfamily protein. In vitrocell-free expression system in combination with its associatedengineered tRNA synthase and tRNA can be utilized to ensure the correctmodification in a specific amino acid position genetically tagged tointroduce non-natural amino acids.

A modified chimera can also be produced, for instance, by amino acidsubstitution, deletion, or addition. For instance, it is reasonable toexpect that an isolated replacement of a leucine with an isoleucine orvaline, an aspartate with a glutamate, a threonine with a serine, or asimilar replacement of an amino acid with a structurally related aminoacid (e.g., conservative mutations) will not have a major effect on thebiological activity of the resulting molecule. Conservative replacementsare those that take place within a family of amino acids that arerelated in their side chains.

An embodiment contemplates making mutations in a proteolytic cleavagesite of the chimera sequence to make the site less susceptible toproteolytic cleavage. Computer analysis (using a commercially availablesoftware, e.g., MacVector, Omega, PCGene, Molecular Simulation, Inc.)can be used to identify proteolytic cleavage sites. As will berecognized by one of skill in the art, most of the described mutations,variants or modifications may be made at the nucleic acid level or, insome cases, by post translational modification or chemical synthesis.Such techniques are well known in the art.

An embodiment contemplates specific mutations of a chimera sequences soas to alter the glycosylation of the chimera. Such mutations may beselected so as to introduce or eliminate one or more glycosylationsites, such as O-linked or N-linked glycosylation sites.Asparagine-linked glycosylation recognition sites generally comprise atripeptide sequence, asparagine-X-threonine (where “X” is any aminoacid) which are specifically recognized by appropriate cellularglycosylation enzymes. The alteration may also be made by the additionof, or substitution by, one or more serine or threonine residues to thesequence of the wild-type polypeptide (for O-linked glycosylationsites). A variety of amino acid substitutions or deletions at one orboth of the first or third amino acid positions of a glycosylationrecognition site (and/or amino acid deletion at the second position)results in non-glycosylation at the modified tripeptide sequence.Another means of increasing the number of carbohydrate moieties is bychemical or enzymatic coupling of glycosides to the polypeptide.Depending on the coupling mode used, the sugar(s) may be attached to (a)arginine and histidine; (b) free carboxyl groups; (c) free sulfhydrylgroups such as those of cysteine; (d) free hydroxyl groups such as thoseof serine, threonine, or hydroxyproline; (e) aromatic residues such asthose of phenylalanine, tyrosine, or tryptophan; or (f) the amide groupof glutamine. These methods are described in WO 87/05330 published Sep.11, 1987, and in Aplin and Wriston (1981) CRC Crit. Rev. Biochem., pp.259-306, incorporated by reference herein. Removal of one or morecarbohydrate moieties present on a chimera may be accomplishedchemically and/or enzymatically. Chemical deglycosylation may involve,for example, exposure to the compound trifluoromethanesulfonic acid, oran equivalent compound. This treatment results in the cleavage of mostor all sugars except the linking sugar (N-acetylglucosamine orN-acetylgalactosamine), while leaving the amino acid sequence intact.Chemical deglycosylation is further described by Hakimuddin et al.(1987) Arch. Biochem. Biophys. 259:52 and by Edge et al. (1981) Anal.Biochem. 118:131. Enzymatic cleavage of carbohydrate moieties onpolypeptides can be achieved by the use of a variety of endo- andexo-glycosidases as described by Thotakura et al. (1987) Meth. Enzymol.138:350. The nucleic acid and/or amino acid sequence of a propeptide maybe adjusted, as appropriate, depending on the type of expression systemused, as mammalian, yeast, insect and plant cells may all introducediffering glycosylation patterns that can be affected by the amino acidsequence of the peptide.

In some embodiments, the chimeric polypeptide can be in the form ofarrays. The polypeptide may be in a soluble form, for example assolutions in the wells of mircotitre plates, or immobilized onto asubstrate. The substrate can be a solid substrate or a porous substrate(e.g, membrane), which can be composed of organic polymers such aspolystyrene, polyethylene, polypropylene, polyfluoroethylene,polyethyleneoxy, and polyacrylamide, as well as co-polymers and graftsthereof. A solid support can also be inorganic, such as glass, silica,controlled pore glass (CPG), reverse phase silica or metal, such as goldor platinum. The configuration of a substrate can be in the form ofbeads, spheres, particles, granules, a gel, a membrane or a surface.Surfaces can be planar, substantially planar, or non-planar. Solidsupports can be porous or non-porous, and can have swelling ornon-swelling characteristics. A solid support can be configured in theform of a well, depression, or other container, vessel, feature, orlocation. A plurality of supports can be configured on an array atvarious locations, addressable for robotic delivery of reagents, or bydetection methods and/or instruments.

An embodiment also provides a polynucleotide encoding the chimericTGF-beta family polypeptide disclosed herein. The polynucleotide may beoperably linked to one or more heterologous regulatory or controlsequences that control gene expression to create a recombinantpolynucleotide capable of expressing the polypeptide. Expressionconstructs containing a polynucleotide encoding the chimeric polypeptidecan be introduced into appropriate host cells to express thepolypeptide. Polynucleotide sequences encoding various domains or fullchimera of an embodiment can be determined without undue efforts basedupon the various codons that are associated with an amino acid of in apolypeptide. Furthermore, an embodiment provides exemplary sequences ofthe TGF-β family member. Deriving the sequences of a domain or chimerafrom the sequences provided herein is readily performed by one of skillin the art. Given the knowledge of specific sequences of the TGF-betafamily of proteins, and the specific descriptions of the chimericpolypeptide herein (e.g., the domain structure of the chimeric domains),the nucleic acid sequence of the engineered chimera will be apparent tothe skilled artisan. The knowledge of the codons corresponding tovarious amino acids coupled with the knowledge of the amino acidsequence of the polypeptide allows those skilled in the art to makedifferent polynucleotides encoding the polypeptide of an embodiment.Thus, an embodiment contemplates each and every possible variation ofthe polynucleotide that could be made by selecting combinations based onpossible codon choices, and all such variations are to be consideredspecifically disclosed for any of the polypeptides described herein.

In some embodiments, the polynucleotide comprises a polynucleotide thatencodes the polypeptide described herein but have about 80% or moresequence identity, about 85% or more sequence identity, about 90% ormore sequence identity, about 91% or more sequence identity, about 92%or more sequence identity, about 93% or more sequence identity, about94% or more sequence identity, about 95% or more sequence identity,about 96% or more sequence identity, about 97% or more sequenceidentity, about 98% or more sequence identity, or about 99% or moresequence identity at the nucleotide level to a reference polynucleotideencoding a chimera or parental TGF-beta family polypeptide.

In some embodiments, the isolated polynucleotide encoding thepolypeptide may be manipulated in a variety of ways to provide forexpression of the polypeptide. Manipulation of the isolatedpolynucleotide prior to its insertion into a vector may be desirable ornecessary depending on the expression vector. The techniques formodifying polynucleotides and nucleic acid sequences utilizingrecombinant DNA methods are well known in the art. Guidance is providedin Sambrook et al., 2001, Molecular Cloning: A Laboratory Manual, 3rdEd., Cold Spring Harbor Laboratory Press; and Current Protocols inMolecular Biology, Ausubel. F. ed., Greene Pub. Associates, 1998,updates to 2007.

In some embodiments, the polynucleotide is operatively linked to controlsequences for the expression of the polynucleotide and/or polypeptide.In some embodiments, the control sequence may be an appropriate promotersequence, which can be obtained from genes encoding extracellular orintracellular polypeptides, either homologous or heterologous to thehost cell.

In some embodiments, the control sequence may also be a suitabletranscription terminator sequence, a sequence recognized by a host cellto terminate transcription. The terminator sequence is operably linkedto the 3′ terminus of the nucleic acid sequence encoding thepolypeptide. Any terminator which is functional in the host cell ofchoice may be used.

In some embodiments, the control sequence may also be a suitable leadersequence, a nontranslated region of an mRNA that is important fortranslation by the host cell. The leader sequence is operably linked tothe 5′ terminus of the nucleic acid sequence encoding the polypeptide.Any leader sequence that is functional in the host cell of choice may beused.

In some embodiments, the control sequence may also be a signal peptidecoding region that codes for an amino acid sequence linked to the aminoterminus of a polypeptide and directs the encoded polypeptide into thecell's secretory pathway. The 5′ end of the coding sequence of thenucleic acid sequence may inherently contain a signal peptide codingregion naturally linked in translation reading frame with the domain ofthe coding region that encodes the secreted polypeptide. Alternatively,the 5′ end of the coding sequence may contain a signal peptide codingregion that is foreign to the coding sequence. The foreign signalpeptide-coding region may be required where the coding sequence does notnaturally contain a signal peptide coding region.

An embodiment is further directed to a recombinant expression vectorcomprising a polynucleotide encoding the chimeric TGF-beta polypeptidedescribed herein, and one or more expression regulating regions such asa promoter and a terminator, a replication origin, etc., depending onthe type of hosts into which they are to be introduced. In creating theexpression vector, the coding sequence is located in the vector so thatthe coding sequence is operably linked with the appropriate controlsequences for expression.

The recombinant expression vector may be any vector (e.g., a plasmid orvirus), which can be conveniently subjected to recombinant DNAprocedures and can bring about the expression of the polynucleotidesequence. The choice of the vector will typically depend on thecompatibility of the vector with the host cell or in vitro cell-freereaction mixture into which the vector is to be introduced. The vectormay be linear or closed circular plasmids.

The expression vector may be an autonomously replicating vector, i.e., avector that exists as an extrachromosomal entity, the replication ofwhich is independent of chromosomal replication, e.g., a plasmid, anextrachromosomal element, a minichromosome, or an artificial chromosome.The vector may contain any means for assuring self-replication.Alternatively, the vector may be one which, when introduced into thehost cell, is integrated into the genome and replicated together withthe chromosome(s) into which it has been integrated. Furthermore, asingle vector or plasmid or two or more vectors or plasmids whichtogether contain the total DNA to be introduced into the genome of thehost cell, or a transposon, may be used.

In some embodiments, the expression vector contains one or moreselectable markers, which permit easy selection of transformed cells. Aselectable marker is a gene the product of which provides for biocide orviral resistance, resistance to heavy metals, prototrophy to auxotrophs,and the like.

An embodiment provides a host cell comprising a polynucleotide encodingthe chimeric TGF-beta polypeptide, the polynucleotide being operativelylinked to one or more control sequences for expression of the fusionpolypeptide in the host cell. Host cells for use in expressing thefusion polypeptide encoded by the expression vector of an embodiment arewell known in the art. Appropriate culture mediums and growth conditionsfor the above-described host cells are well known in the art.

An expression vector can be designed for expression of a chimera inprokaryotic or eukaryotic cells. For example, a chimera of an embodimentcan be expressed in bacterial or prokaryote cells such as E. Coli,insect cells (e.g., the baculovirus expression system), yeast cells,microalgae, plant cells or mammalian cells as well as in vitro cell-freeexpression system. Some suitable host cells are discussed further inGoeddel, Gene Expression Technology: Methods in Enzymology 185, AcademicPress, San Diego, Calif. (1990).

While one example of an expression system discussed is an E. coliexpression system, to those skilled in the art, these proteins can beeasily be cloned into and expressed from a large number of otherexpression systems. The advantages include, but are not limited to,achieving post-translational modifications as would be seen in theorganism the protein was derived from (in this case H. sapiens),expression of the ligands without the start methionine required forbacterial expression, and easy incorporation of non-natural amino acidsor additional chemical modifications. Suitable prokaryotes include butare not limited to eubacteria, such as Gram-negative or Gram-positiveorganisms, for example, Enterobacteriaceae such as E. coli. Various E.coli strains are publicly available, such as E. coli K12 strain MM294(ATCC 31,446); E. coli X1776 (ATCC 31.537); E. coli strain W3110 (ATCC27,325) and K5 772 (ATCC 53,635). In addition to prokaryotes, eukaryoticmicrobes such as filamentous fungi or yeast are suitable cloning orexpression hosts for VEGF-E-encoding vectors. Saccharomyces cerevisiaeis a commonly used lower eukaryotic host microorganism.

Suitable host cells for the expression of a chimera are derived fromunicellular and multicellular organisms. Examples of invertebrate cellsinclude insect cells such as Drosophila S2 and Spodoptera Sf9, as wellas plant cells. Plant expression systems have also been usedsuccessfully to express modified proteins. Examples of useful mammalianhost cell lines include Chinese hamster ovary (CHO) and COS cells. Morespecific examples include monkey kidney CV1 line transformed by SV40(COS-7, ATCC CRL 1651); human embryonic kidney line (293 or 293 cellssubcloned for growth in suspension culture, Graham et al., J. GenVirol., 36:59 (1977)); Chinese hamster ovary cells/DHFR(CHO, Urlaub andChasin, Proc. Natl. Acad. Sci. USA, 77:4216 (1980)); mouse Sertoli cells(TM4, Mather, Biol. Reprod., 23:243-251 (1980)); human lung cells (W138,ATCC CCL 75); human liver cells (Hep G2, HB 8065); and mouse mammarytumor (MMT 060562, ATCC CCL51). The selection of the appropriate hostcell is deemed to be within the skill in the art.

Alternate protein expression systems include human embryonic kidney(HEK) 293 cells, insect cell line (S. frugiperda) utilizing thebaculovirus expression system, yeast expression systems not limited toP. pastoris and S. cerevisiae, and numerous Microalgae strains.Transgenic animals can be used to express correctly modified protein.

In essence, the animals become living ‘bioreactors’ capable ofexpressing large amounts of the desired protein in an easily harvestedfluid or tissue, such as the milk from a cow. Cell-free in vitroexpression systems using either the bacterial or wheat germ cell lysatecan be employed. Cell-free expression system will permit inserting awide range of non-natural amino acids or epitope tags with higherefficiency and greater specificity.

Examples of bacterial vectors include pQE70, pQE60, pQE-9 (Qiagen), pBS,pD10, phagescript, psiX174, pbluescript SK, pbsks, pNH8A, pNH16a,pNH18A, pNH46A (Stratagene); ptrc99a, pKK223-3, pKK233-3, pDR540, andpRIT5 (Pharmacia). Examples of vectors for expression in the yeast S.cerevisiae include pYepSec1 (Baldari et al., EMBO J. 6:229 (1987)), pMFa(Kurjan and Herskowitz, Cell 30:933 (1982)), pJRY88 (Schultz et al.,Gene 54:113 (1987)), and pYES2 (Invitrogen Corporation, San Diego,Calif.). Baculovirus vectors available for expression of nucleic acidsto produce proteins in cultured insect cells (e.g., Sf9 cells) includethe pAc series (Smith et al., Mol. Cell. Biol. 3:2156 (1983)) and thepVL series (Lucklow and Summers Virology 170:31 (1989)).

Examples of mammalian expression vectors include pWLNEO, pSV2CAT, pOG44,pXT1, pSG (Stratagene) pSVK3, PBPV, pMSG, PSVL (Pharmacia), pCDM8 (Seed,Nature 329:840 (1987)) and pMT2PC (Kaufman et al., EMBO J. 6:187(1987)). When used in mammalian cells, the expression vector's controlfunctions are often provided by viral regulatory elements. For example,commonly used promoters are derived from polyoma, adenovirus 2,cytomegalovirus and Simian Virus 40.

Viral vectors have been used in a wide variety of gene deliveryapplications in cells, as well as living animal subjects. Viral vectorsthat can be used include, but are not limited to, retrovirus,lentivirus, adeno-associated virus, poxyvirus, alphavirus, baculovirus,vaccinia virus, herpes virus. Epstein-Barr virus, adenovirus,geminivirus, and caulimovims vectors. Non-viral vectors includeplasmids, liposomes, electrically charged lipids (cytofectins), nucleicacid-protein complexes, and biopolymers. In addition to a nucleic acidof interest, a vector may also comprise one or more regulatory regions,and/or selectable markers useful in selecting, measuring, and monitoringnucleic acid transfer results (delivery to specific tissues, duration ofexpression, etc.).

The chimera of an embodiment can be made by using methods well known inthe art. A polynucleotide can be synthesized by recombinant techniques,such as that provided in Sambrook et al., 2001, Molecular Cloning: ALaboratory Manual, 3rd Ed., Cold Spring Harbor Laboratory Press; andCurrent Protocols in Molecular Biology, Ausubel. F. ed., Greene Pub.Associates, 1998, updates to 2007. Polynucleotides encoding the enzymes,or the primers for amplification can also be prepared by standardsolid-phase methods, according to known synthetic methods, for exampleusing phosphoramidite method described by Beaucage et al., (1981) TetLett 22:1859-69, or the method described by Matthes et al., (1984) EMBOJ. 3:801-05, e.g., as it is typically practiced in automated syntheticmethods. In addition, automated peptide synthesizers are commerciallyavailable (e.g., Advanced ChemTech Model 396; Milligen/Bioscarch 9600).

An embodiment is directed to a method to accelerate construction oflarge chimera libraries. Accordingly, an embodiment provides arecombinant strategy termed RASCH (RAndom Segmental CHimera). It uses atemplate sequence (first strand from one TGF-beta superfamily member)and a few target sequences (second (third, fourth, fifth, sixth) strandfrom one or more alternate TGF-beta superfamily members), whose domainsare to be linked. The template DNA sequence is used to promote efficientcoupling of the target sequences and is degraded once domains arelinked. Following the gene construction to create the chimericsequences, the new ligands are chemically refolded into functionaldimer. This dimerization process permits additional diversification ofthe final sequence by mixing and dimerizing two different sequences ofboth natural and designer origins. Therefore, the RASCH method can beused to diversify the approximate 40 natural protein sequences ofTGF-beta superfamily ligands into ten of thousands or more variantsequences, each distinct from any naturally-occurring TGF-betasuperfamily ligand sequences.

Engineered polypeptide expressed in a host cell can be recovered fromthe cells and or the culture medium using any one or more of thewell-known techniques for protein purification, including, among others,lysozyme treatment, sonication, filtration, salting-out,ultra-centrifugation, chromatography, and affinity separation (e.g.,substrate bound antibodies).

Chromatographic techniques for isolation of the polypeptide include,among others, reversed phase chromatography high performance liquidchromatography, ion exchange chromatography, gel electrophoresis, andaffinity chromatography. Conditions for purifying a particular enzymewill depend, in part, on factors such as net charge, hydrophobicity,hydrophilicity, molecular weight, molecular shape, etc., and will beapparent to those having skill in the art.

Assays to determine activity are well known in the art. An embodimentrelates to assays to test for biological activity of chimeric proteins,more preferably, to assays to test for clinical activity. Such activitycan include enhanced agonistic or antagonistic TGF-beta activity,combined or novel biological activity, and the like.

In certain embodiments, a chimeric protein of an embodiment comprisingan agonist of a TGF-beta superfamily protein comprises an antagonist ofa different TGF-beta superfamily protein.

Irrespective of which protein expression, harvesting, and, foldingmethodologies are used, certain of the subject chimeric proteins canbind, preferentially to a pre-selected receptor and can now beidentified using standard methodologies, e.g., ligand/receptor bindingassays, well known, and thoroughly documented in the art. See, e.g.,Legerski gl al. (1992) Bio h_Biophys. Res. Comm. 183: 672679; Frakar etal. (1978) Biochem. Bio12-hys. Res. Comm 80:849-857; Chio et el. (1990)Nature 343: 266-269; Dahlman et al. (1988) Biochem 27: 1813-1817;Strader et el. (1989) J. Biol. Chem. 264: 13572-13578; and DDowd et al.(1988) J. Biol. Chem. 263: 15985-15992.

Typically, in a ligand/receptor binding assay, the native or parentTGF-beta superfamily member of interest having a known, quantifiableaffinity for a pre-selected receptor is labeled with a detectablemoiety, for example, a radiolabel, a chromogenic label, or a fluorogeniclabel. Aliquots of purified receptor, receptor binding domain fragments,or cells expressing the receptor of interest on their surface areincubated with the labeled TGF-beta superfamily member in the presenceof various concentrations of the unlabeled chimeric protein. Therelative binding affinity of a candidate chimeric protein may bemeasured by quantitating the ability of the chimeric protein to inhibitthe binding of the labeled TGF-beta superfamily member with thereceptor. In performing the assay, fixed concentrations of the receptorand the TGF-beta superfamily member are incubated in the presence andabsence of unlabeled chimeric protein. Sensitivity may be increased bypreincubating the receptor with the chimeric protein before adding thelabeled template TGF-beta superfamily member. After the labeledcompetitor has been added, sufficient time is allowed for adequatecompetitor binding, and then free and bound labeled TGF-beta superfamilymembers are separated from one another, and one or the other measured.Labels useful in the practice of the screening procedures includeradioactive labels, chromogenic labels, spectroscopic labels such asthose disclosed in Haughland (1994) “Handbook of Fluorescent andResearch Chemicals,” 5 ed. by Molecular Probes, Inc., Eugene, Oreg., orconjugated enzymes having high turnover rates, i.e., horseradishperoxidase, alkaline phosphatase, or agalactosidase, used in combinationwith chemiluminescent or fluorogenic substrates. The biologicalactivity, namely the agonist or antagonist properties of the resultingchimeric protein constructs can subsequently be characterized usingconventional in vivo and in vitro assays that have been developed tomeasure the biological activity of any TGF-beta superfamily member. Itis appreciated, however, the type of assay used preferably depends onthe TGF-beta superfamily member upon which the chimeric protein is based

The presence of multimers among the subject chimeric proteins can bedetected visually either by standard SDS-PAGE in the absence of areducing agent such as DTT or by HPLC (e.g., C18 reverse phase HPLC).Multimeric proteins of an embodiment can have an apparent molecularweight proportionally greater than the monomeric subunit, e.g., in therange about 28-36 kDa for a dimer, as compared to monomeric subunits,which may have an apparent molecular weight of about 14-18 kDa. Themultimeric protein can readily be visualized on an electrophoresis gelby comparison to commercially available molecular weight standards. Thedimeric protein also elutes from a C18 RP HPLC (45-50% acetonitrile:0.1%TFA) at a time point different from that for its monomeric counterpart.

A second assay evaluates the presence of dimer (e.g., OP-1 dimers) byits ability to bind to hydroxyapatite. Optimally-folded dimer binds ahydroxyapatite column well in pH7, 10 mM phosphate, 6M urea, and 0.142MNaCl (dimer elutes at 0.25 M NaCl) as compared to monomer, which doesnot bind substantially at those concentrations (monomer elutes at 0.1MNaCl). A third assay evaluates the presence of dimer by the protein'sresistant to trypsin or pepsin digestion. The folded dimeric species issubstantially resistant to both enzymes, particularly trypsin, whichcleaves only a small portion of the N-terminus of the mature protein,leaving a biologically active dimeric species only slightly smaller insize than the untreated dimer (each monomer in amino acids smaller aftertrypsin cleavage). By contrast, the monomers and misfolded dimers aresubstantially degraded. In the assay, the protein is subjected to anenzyme digest using standard conditions, e.g., digestion in a standardbuffer such as 50 mM Tris buffer, pH 8, containing 4 M urea, 100 mMNaCl, 0.3% Tween-80 and 20 mM methylamine. Digestion is allowed to occurat 37° C. for on the order of 16 hours, and the product visualized byany suitable means, preferably SDS PAGE.

The biological activity of the subject chimeric proteins, for example,the chimeric proteins having one or more domains from BMPs, can beassessed by any of a number of means as described in WO00/20607. Forexample, the protein's ability to induce endochondral bone formation canbe evaluated using the well characterized rat subcutaneous bone assay.In the assay bone formation is measured by histology, as well as byalkaline phosphatase and/or osteoclacin production. In addition,osteogenic proteins having high specific bone forming activity, such asOP-1, BMP-2, BMR4, BMP-5 and BMP-6, also induce alkaline phosphataseactivity in an in vitro rat osteoblast or osteosarcoma cell-based assay.Such assays are well described in the art. See, for example, Sabokdar ofal. (1994) Bone and Mineral 27:57-67; Knutsen et al. (1993) BiochemBiophys Res. Commun 194:1352-1358; and Maliakal et al. (1994) GrowthFactors 1:227-234).

By contrast, osteogenic proteins having low specific bone formingactivity, such as CDMP-1 and CDMP-2, for example, do not induce alkalinephosphatase activity in the cell based osteoblast assay. For example,CDMP-1. CDMP-2 and CMDP-3 all are competent to induce bone formation,although with a lower specific activity than BMP-2, BW-4, BV-5, BMP-6 orOP-1. Conversely, BMP-2, BMP-4, BMP-5, BPyIP-6 and OP-1 all can inducearticular cartilage formation, albeit with a lower specific activitythan CDMP-1, CDMP-2 or CDMP-3. Accordingly, a chimeric protein havingone or more domain from CDMP, designed and described herein to be achimeric protein competent to induce alkaline phosphatase activity inthe cell-based assay, is expected to demonstrate a higher specific boneforming activity in the rat animal bioassay.

The chimeric protein's biological activity can also be readily evaluatedby the protein's ability to inhibit epithelial cell growth. A useful,well characterized in vitro assay utilizes mink lung cells or melanomacells. See WO00/20607. Other assays for other members of the TGF-betasuperfamily are well described in the literature and can be performedwithout undue experimentation.

An embodiment provides methods and agents for control and maintainskeletal muscle mass in a host, preferably a human. Therefore, anychimeric protein of an embodiment that is expected to affectmuscle-related function of a TGF-beta superfamily protein such as forexample GDF-8 can be tested in whole cells or tissues, in vitro or invivo, to confirm their ability to modulate skeletal muscle mass. GDF-8(also known as myostatin) is a negative regulator of skeletal musclegrowth. GDF-8 knockout mice have approximately twice the skeletal musclemass of normal mice. The effects of increased muscle mass on bonemodeling may be investigated, e.g., by examining bone mineral content(BMC) and bone mineral density (BMD) in the femora of female GDF-8knockout mice. Dual-energy X-ray absorptiometry (DEXA) densitometry canbe used to measure whole-femur BMC and BMD, and PQCT densitometry can beused to calculate BMC and BMD from cross-sections of tissues. Hamrick,Anat Rec. 2003 May; 272A(1):388-91. As is known in the art, a chimericprotein of an embodiment may be introduced into the GDF-8 knockout mice,and similar assays can be used to determine the effect of the chimericprotein on skeletal muscle mass and bone density.

The dystrophic phenotype in the mdx mouse model of Duchenne musculardystrophy (DMD) may also be employed to test the biological activity ofa chimeric protein of an embodiment. It was reported that blockade ofendogenous myostatin by using intraperitoneal injections of blockingantibodies for three months resulted in an increase in body weight,muscle mass, muscle size and absolute muscle strength in mdx mousemuscle along with a significant decrease in muscle degeneration andconcentrations of serum creatine kinase. Bogdanovich et al., Nature.2002 Nov. 28; 420(6914):418-21. Similar study may be employed todetermine whether a chimeric protein of an embodiment potentiates orinhibits the endogenous GDF-8 activity.

An embodiment provides methods and agents for modulating neurogenesis.For example, GDF-11 is known to inhibit olfactory epitheliumneurogenesis in vitro by inducing p27(Kip1) and reversible cell cyclearrest in progenitors. Wu et al. Neuron. 2003 Jan. 23; 37(2): 197-207.The effect of a chimeric protein of an embodiment on neurogenesis can besimilarly tested. Further, the effect of a chimeric protein of anembodiment on GDF-11's effect on neurogenesis can also be tested usingsimilar assays as described in Wu et al. Id.

An embodiment provides methods and agents for stimulating bone formationand increasing bone mass. Therefore, any chimeric protein of anembodiment that is expected to affect bone-related function of aTGF-beta superfamily protein such as for example BMP-2, BMP-3, GDF-10,BMP-4, BMP-7, or BMP-8, can be tested in whole cells or tissues, invitro or in vivo, to confirm their ability to modulate bone or cartilagegrowth. Various methods known in the art can be utilized for thispurpose.

For example, BMP-3 inhibits BMP2-mediated induction of Msx2 and blocksBMP2-mediated differentiation of osteoprogenitor cells into osteoblasts.Thus, the effect of a subject chimer protein, preferably one comprisinga domain from a BMP-2 or BMP-3, on bone or cartilage growth can bedetermined by their effect on the osteogenic activity of BMP-2, forexample, by measuring induction of Msx2 or differentiation ofosteoprogenitor cells into osteoblasts in cell based assays (see, e.g.,Daluiski et al., Nat. Genet. 2001, 27(1):84-8; Hino et al., FrontBiosci. 2004, 9:1520-9). Similarly, a subject chimeric protein,preferably one comprising a domain from a BMP-2 or BMP-3, may be testedfor its osteogenic or anti-osteogenic activity or its agonistic orantagonistic effect on BMP-2-mediated osteogenesis.

Another example of cell-based assays includes analyzing the osteogenicor anti-osteogenic activity of a subject chimeric and test compounds inmesenchymal progenitor and osteoblastic cells. To illustrate,recombinant adenoviruses expressing a subject chimeric protein wereconstructed to infect pluripotent mesenchyimal progenitor C3H10T1/2cells, preosteoblastic C2C12 cells, and osteoblastic TE-85 cells.Osteogenic activity is then determined by measuring the induction ofalkaline phosphatase, osteocalcin, and matrix mineralization (see, e.g.,Cheng et al., J bone Joint Surg Am. 2003, 85-A(8): 1544-52).

Further, an embodiment contemplates in vivo assays to measure bone orcartilage growth. For example, Namkung-Matthai et al., Bone, 28:80-86(2001) discloses a rat osteoporotic model in which bone repair duringthe early period after fracture is studied. Kubo et al., SteroidBiochemistry & Molecular Biology, 68:197-202 (1999) also discloses a ratosteoporotic model in which bone repair during the late period afterfracture is studied. These references are incorporated by referenceherein in their entirety for their disclosure of rat model for study onosteoporotic bone fracture. In certain aspects, an embodiment makes useof fracture healing assays that are known in the art. These assaysinclude fracture technique, histological analysis, and biomechanicalanalysis, which are described in, for example, U.S. Pat. No. 6,521,750,which is incorporated by reference in its entirety for its disclosure ofexperimental protocols for causing as well as measuring the extent offractures, and the repair process.

It is understood that the screening assay of an embodiment apply to notonly the subject chimeric proteins and variants thereof, but also anytest compounds including agonists and antagonist of the chimericproteins or their variants themselves. Further, these screening assaysare useful for drug target verification and quality control purposes.

An embodiment relates to the use of the subject chimeric TGF-betasuperfamily proteins to identify compounds which can modulate activitiesof the chimeric proteins. Compounds identified through this screeningcan be tested in tissues (e.g., bone and/or cartilage) or cells (e.g.,muscle cells) to assess their ability to modulate the test tissues orcells (e.g., bone/cartilage growth or muscle cell growth) in vitro.Optionally, these compounds can further be tested in animal models toassess their ability to modulate, e.g., bone/cartilage growth or musclecontrol and maintenance in vivo.

A variety of assay formats will suffice and, in light of the presentinvention, those not expressly described herein will nevertheless becomprehended by one of ordinary skill in the art. As described herein,the test compound (agent) of an embodiment may be created by anycombinatorial chemical method. Alternatively, the subject compounds maybe naturally occurring biomolecules synthesized in vivo or in vitro.Compounds (agents) to be tested for their ability to act as modulatorsof bone or cartilage growth can be produced, for example, by bacteria,yeast, plants or other organisms (e.g., natural products), producedchemically (e.g., small molecules, including peptidomimetics), orproduced recombinantly. Test compound contemplated by an embodimentinclude non-peptidyl organic molecules, peptides, polypeptides,peptidomimetics, sugars, hormones, and nucleic acid molecules. In aspecific embodiment, the test agent is a small organic molecule having amolecular weight of less than about 2,000 daltons.

The test compound of an embodiment can be provided as single, discreteentities, or provided in libraries of greater complexity, such as madeby combinatorial chemistry. These libraries can comprise, for example,alcohols, alkyl halides, amines, amides, esters, aldehydes, ethers andother classes of organic compounds. Presentation of test compounds tothe test system can be in either an isolated form or as mixtures ofcompounds, especially in initial screening steps. Optionally, thecompounds may be optionally derivatized with other compounds and havederivatizing groups that facilitate isolation of the compounds.Non-limiting examples of derivatizing groups include biotin,fluorescein, digoxygenin, green fluorescent protein, isotopes,polyhistidine, magnetic beads, glutathione S transferase,photoactivatible crosslinkers or any combinations thereof.

In many drug screening programs which test libraries of compounds andnatural extracts, high throughput assays are desirable in order tomaximize the number of compounds surveyed in a given period of time.Assays which are performed in cell-free systems, such as may be derivedwith purified or semi-purified proteins, are often preferred as“primary” screens in that they can be generated to permit rapiddevelopment and relatively easy detection of an alteration in amolecular target which is mediated by a test compound. Moreover, theeffects of cellular toxicity or bioavailability of the test compound canbe generally ignored in the in vitro system, the assay instead beingfocused primarily on the effect of the drug on the molecular target asmay be manifest in an alteration of binding affinity between a chimericTGF-beta superfamily protein and its binding protein (e.g., the chimericprotein itself or a TGF-beta receptor protein or fragments thereof).

Merely to illustrate, in an exemplary screening assay of an embodiment,the compound of interest is contacted with an isolated and purifiedchimeric protein which is ordinarily capable of binding to a TGF-betareceptor protein or fragments thereof, as appropriate for the intentionof the assay. To the mixture comprising a subject chimeric protein and aTGF-beta receptor protein is then added a composition containing a testcompound. Detection and quantification of the chimeric protein receptorcomplexes provides a means for determining the compound's efficacy atinhibiting (or potentiating) complex formation between the chimericTGF-beta superfamily protein and its binding protein, e.g., the TGF-betareceptor or fragments thereof. The efficacy of the compound can beassessed by generating dose response curves from data obtained usingvarious concentrations of the test compound. Moreover, a control assaycan also be performed to provide a baseline for comparison. For example,in a control assay, an isolated and purified chimeric TGF-betasuperfamily protein is added to a composition (cell-free or cell-based)containing a TGF-beta receptor protein or fragment thereof, and theformation of the chimeric protein-receptor complex is quantitated in theabsence of the test compound. It will be understood that, in general,the order in which the reactants may be admixed can be varied, and canbe admixed simultaneously. Moreover, in place of purified proteins,cellular extracts and lysates may be used to render a suitable cell-freeassay system. Alternatively, cells expressing a TGF-beta receptorprotein or fragments thereof on their surfaces can be used in certainassays.

Complex formation between a subject chimeric TGF-beta superfamilyprotein and its binding protein may be detected by a variety oftechniques. For instance, modulation of the formation of complexes canbe quantitated using, for example, detectably labeled proteins such asradiolabelled (e.g., 32P, 35S, 14C or 3H), fluorescently labeled (e.g.,FITC), or enzymatically labeled chimeric protein or its binding protein,by immunoassay, or by chromatographic detection.

An embodiment contemplates the use of fluorescence polarization assaysand fluorescence resonance energy transfer (FRET) assays in measuring,either directly or indirectly, the degree of interaction between achimeric TGF-beta superfamily protein and its binding protein (e.g., aTGF-beta receptor protein or fragments thereof). Further, other modes ofdetection such as those based on optical waveguides (PCT Publication WO96/26432 and U.S. Pat. No. 5,677,196), surface plasmon resonance (SPR),surface charge sensors, and surface force sensors are compatible withmany embodiments of the present invention.

Moreover, an embodiment contemplates the use of an interaction trapassay, also known as the “two hybrid assay,” for identifying agents thatdisrupt or potentiate interaction between a chimeric TGF-betasuperfamily protein and its binding protein (e.g., a TGF-beta receptorprotein or fragments thereof). See for example, U.S. Pat. No. 5,283,317;Zervos et al. (1993) Cell 72:223-232; Madura et al. (1993) J Biol Chem268:12046-12054; Bartel et al. (1993) Biotechniques 14:920-924; andIwabuchi et al. (1993) Oncogene 8:1693-1696).

A chimera polynucleotide, a polypeptide, an antibody, a cell and otherreagent of an embodiment have a wide variety of uses, both in vitro andin vivo. For example, in representative embodiments, these reagents maybe used in vitro or in vivo (e.g., in an animal model) (o study theprocesses of mineralization, bone formation, and bone loss. Further,“knock in” and “knock out” animals can be used as animal models ofdisease or as screening tools (discussed more below) for compounds thatinteract with the chimera polynucleotide or polypeptide. It will beapparent to those skilled in the art that any suitable vector can beused to deliver the polynucleotide to a cell or subject. The choice ofdelivery vector can be made based on a number of factors known in theart, including age and species of the target host, in vitro versus invivo delivery, level and persistence of expression desired, intendedpurpose (e.g., for therapy or screening), the target cell or organ,route of delivery, size of the isolated polynucleotide, safety concerns,and the like.

Chimeric polypeptide of an embodiment may be formulated for use invarious biological systems including in vivo. Any of a variety ofart-known methods can be used to administer a chimera either alone or incombination with other active agents. For example, administration can beparenterally by injection or by gradual infusion over time. The agent(s) can be administered by such means as oral, rectal, buccal (e.g.,sublingual), vaginal, parenteral (e.g., subcutaneous, intramuscularincluding skeletal muscle, cardiac muscle, diaphragm muscle and smoothmuscle, intradermal, intravenous, intraperitoneal), topical (i.e., bothskin and mucosal surfaces, including airway surfaces), intranasal,transdermal, intraarticular, intrathecal, intracavity, and inhalationadministration, administration to the liver by intraportal delivery, aswell as direct organ injection (e.g., into the liver, into the brain fordelivery to the central nervous system, into the pancreas). The mostsuitable route in any given case will depend on the nature and severityof the condition being treated and on the nature of the particularcompound which is being used.

An embodiment also provides a pharmaceutical preparation comprising asubject chimeric protein and a pharmaceutically acceptable carrier. Apharmaceutical preparation may be employed to promote growth of a tissueor diminishing or prevent loss of a tissue in a subject, preferably ahuman. The targeted tissue can be, for example, bone, cartilage,skeletal muscle, cardiac muscle and/or neuronal tissue.

In another aspect, a chimeric TGF-beta polypeptide can be formulatedeither alone or in combination with other agents for administration(e.g., as a lotion, cream, spray, gel, or ointment). It may beformulated into liposomes to reduce toxicity or increasebioavailability. Other methods for delivery include oral methods thatentail encapsulation of the in microspheres or proteinoids, aerosoldelivery (e.g., to the lungs), or transdermal delivery (e.g., byiontophoresis or transdermal electroporation). Other methods ofadministration will be known to those skilled in the art.

Preparations for parenteral administration of a composition comprising achimeric TGF-beta polypeptide include sterile aqueous or non-aqueoussolutions, suspensions, and emulsions. Examples of non-aqueous solventsare propylene glycol, polyethylene glycol, vegetable oils (e.g., oliveoil), and injectable organic esters such as ethyl oleate. Examples ofaqueous carriers include water, saline, and buffered media,alcoholic/aqueous solutions, and emulsions or suspensions. Examples ofparenteral vehicles include sodium chloride solution, Ringer's dextrose,dextrose and sodium chloride, lactated Ringer's, and Fixed oils.Intravenous vehicles include fluid and nutrient replenishers,electrolyte replenishers (such as those based on Ringer's dextrose), andthe like. Preservatives and other additives such as, otherantimicrobial, anti-oxidants, cheating agents, inert gases and the likealso can be included.

An embodiment provides various disease and disorders that may bemodulated by a TGF-beta protein family member comprising contacting oradministering a therapeutically effective amount of a chimeric TGF-betapolypeptide either alone or in combination with other agents to asubject who has, or is at risk of having, such a disorder.

A therapeutically effective amount can be measured as the amountsufficient to decrease a subject's symptoms associated with the diseasesor disorder. Typically, the subject is treated with an amount of atherapeutic composition sufficient to reduce a symptom of a disease ordisorder by at least 50%, 90% or 100%. Generally, the optimal dosagewill depend upon the disorder and factors such as the weight of thesubject, the age, the weight, sex, and degree of symptoms. For example,with respect to bone morphogenesis, optionally, the dosage may vary withthe type of matrix used in the reconstitution and the types of compoundsin the composition. The addition of other known growth factors to thefinal composition, may also affect the dosage. Progress can be monitoredby periodic assessment of bone growth and/or repair, for example,X-rays, histomorphometric determinations, and tetracycline labeling.Nonetheless, suitable dosages can readily be determined by one skilledin the art. Typically, a suitable dosage is 0.01 to 40 mg/kg bodyweight, e.g.

As mentioned previously, the composition and the method of an embodimentcan include the use of additional (e.g., in addition to a chimericTGF-beta polypeptide) therapeutic agents (e.g., an inhibitor of TNF, anantibiotic, and the like). The chimeric TGF-beta polypeptide, othertherapeutic agent(s), and/or antibiotic(s) can be administered,simultaneously, but may also be administered sequentially.

A pharmaceutical composition comprising a chimera according to anembodiment can be in a form suitable for administration to a subjectusing carriers, excipients, and additives or auxiliaries. Frequentlyused carriers or auxiliaries include magnesium carbonate, titaniumdioxide, lactose, mannitol and other sugars, talc, milk protein,gelatin, starch, vitamins, cellulose and its derivatives, animal andvegetable oils, polyethylene glycols and solvents, such as sterilewater, alcohols, glycerol, and polyhydric alcohols. Intravenous vehiclesinclude fluid and nutrient replenishers. Preservatives includeantimicrobial, anti-oxidants, chelating agents, and inert gases. Otherpharmaceutically acceptable carriers include aqueous solutions,non-toxic excipients, including salts, preservatives, buffers and thelike, as described, for instance, in Remington's PharmaceuticalSciences, 15th ed., Easton: Mack Publishing Co., 1405-1412, 1461-1487(1975), and The National Formulary XIV., 14th ed., Washington: AmericanPharmaceutical Association (1975), the contents of which are herebyincorporated by reference. The pH and exact concentration of the variouscomponents of the pharmaceutical composition are adjusted according toroutine skills in the art. See Goodman and Gilman's, The PharmacologicalBasis for Therapeutics (7th ed.).

The pharmaceutical composition according to an embodiment may beadministered locally or systemically. A “therapeutically effective dose”is the quantity of an agent according to an embodiment necessary toprevent, to cure, or at least partially arrest a symptoms associatedwith a disease or disorder or to promote cell growth, proliferation ordifferentiation. Amounts effective for this use will, of course, dependon the severity of the disease, disorder, or desired effect and willdepend on weight and general state of the subject. Typically, dosagesused in vitro may provide useful guidance in the amounts useful for insitu administration of the pharmaceutical composition, and animal modelsmay be used to determine effective dosages for treatment of the diseaseor disorder. Various considerations are described, e.g., in Langer,Science, 249: 1527, (1990): Gilman et al. (eds.) (1990), each of whichis herein incorporated by reference. Dosages of pharmaceutically activecompounds can be determined by methods known in the art, see, e.g.,Remington's Pharmaceutical Sciences (Maack Publishing Co., Easton. Pa.);Remington. The Science & Practice of Pharmacy, (Lippincott Williams &Wilkins; Twenty first Edition). The therapeutically effective dosage ofany specific compound will vary somewhat from compound to compound, andpatient to patient, and will depend upon the condition of the patientand the route of delivery. As a general proposition, a dosage from about0.1 to about 100 mg/kg will have therapeutic efficacy, with all weightsbeing calculated based upon the weight of the compound, including thecases where a salt is employed. Toxicity concerns at the higher levelcan restrict intravenous dosages to a lower level such as up to about 10to about 20 mg/kg, with all weights being calculated based upon theweight of the compound, including the cases where a salt is employed. Adosage from about 10 mg/kg to about 50 mg/kg can be employed for oraladministration. Typically, a dosage from about 0.5 mg/kg to 15 mg/kg canbe employed for intramuscular injection. Particular dosages are about 1μmol/kg to 50 μmol/kg, and more particularly to about 22 μmol/kg and to33 μmol/kg of the compound for intravenous or oral administration,respectively.

In an embodiment, more than one administration (e.g., two, three, four,or more administrations) can be employed over a variety of limeintervals (e.g., hourly, daily, weekly, monthly, etc.) to achievetherapeutic effects.

The composition and chimera of an embodiment find use in veterinary andmedical applications. Suitable subjects include both avians and mammals,with mammals being preferred. The term “avian” as used herein includes,but is not limited to, chickens, ducks, geese, quail, turkeys, andpheasants. The term “mammal” as used herein includes, but is not limitedto, humans, bovines, ovines, caprines, equines, felines, canines,lagomorphs, etc. Human subjects include neonates, infants, juveniles,and adults. In other embodiments, the subject is an animal model of aliver disease or a bone and cartilage disease.

As used herein, “administering a therapeutically effective amount” isintended to include methods of giving or applying a pharmaceuticalcomposition of an embodiment to a subject that allow the composition toperform its intended therapeutic function.

The pharmaceutical composition can be administered in a convenientmanner, such as by injection (subcutaneous, intravenous, etc.), oraladministration, inhalation, transdermal application, or rectaladministration. Depending on the route of administration, thepharmaceutical composition can be coated with a material to protect thepharmaceutical composition from the action of enzymes, acids, and othernatural conditions that may inactivate the pharmaceutical composition.The pharmaceutical composition can also be administered parenterally orintraperitoneally. Dispersions can also be prepared in glycerol, liquidpolyethylene glycols, and mixtures thereof, and in oils. Under ordinaryconditions of storage and use, these preparations may contain apreservative to prevent the growth of microorganisms.

Pharmaceutical compositions suitable for injectable use include sterileaqueous solutions (where water soluble) or dispersions and sterilepowders for the extemporaneous preparation of sterile injectablesolutions or dispersions. In all cases, the composition should besterile and should be fluid to the extent that easy syringabilityexists. The carrier can be a solvent or dispersion medium containing,for example, water, ethanol, polyol (for example, glycerol, propyleneglycol, and liquid polyethylene glycol, and the like), suitable mixturesthereof, and vegetable oils. The proper fluidity can be maintained, forexample, by the use of a coating, such as lecithin, by the maintenanceof the required particle size, in the case of dispersion, and by the useof surfactants. Prevention of the action of microorganisms can beachieved by various antibacterial and antifungal agents, for example,parabens, chlorobutanol, phenol, ascorbic acid, thimerosal, and thelike. In many cases, it will be typical to include isotonic agents, forexample, sugars, polyalcohols, such as mannitol, sorbitol, or sodiumchloride in the composition. Prolonged absorption of the injectablecomposition can be brought about by including in the composition anagent that delays absorption, for example, aluminum monostearate andgelatin.

Sterile injectable solutions can be prepared by incorporating thepharmaceutical composition in the required amount in an appropriatesolvent with one or a combination of ingredients enumerated above, asrequired, followed by filtered sterilization. Generally, dispersions areprepared by incorporating the pharmaceutical composition into a sterilevehicle that contains a basic dispersion medium and the required otheringredients from those enumerated above.

The pharmaceutical composition can be orally administered, for example,with an inert diluent or an assailable edible carrier. Thepharmaceutical composition and other ingredients can also be enclosed ina hard or soft-shell gelatin capsule, compressed into tablets, orincorporated directly into the individual's diet. For oral therapeuticadministration, the pharmaceutical composition can be incorporated withexcipients and used in the form of ingestible tablets, buccal tablets,troches, capsules, elixirs, suspensions, syrups, wafers, and the like.Such compositions and preparations should contain at least 1% by weightof active compound. The percentage of the compositions and preparationscan, of course, be varied and can conveniently be between about 5% toabout 80% of the weight of the unit.

The tablets, troches, pills, capsules, and the like can also contain thefollowing: a binder, such as gum gragacanth, acacia, corn starch, orgelatin; excipients such as dicalcium phosphate; a disintegrating agent,such as corn starch, potato starch, alginic acid, and the like; alubricant, such as magnesium stearate; and a sweetening agent, such assucrose, lactose or saccharin, or a flavoring agent such as peppermint,oil of wintergreen, or cherry flavoring. When the dosage unit form is acapsule, it can contain, in addition to materials of the above type, aliquid carrier. Various other materials can be present as coatings or tootherwise modify the physical form of the dosage unit. For instance,tablets, pills, or capsules can be coated with shellac, sugar, or both.A syrup or elixir can contain the agent, sucrose as a sweetening agent,methyl and propylparabens as preservatives, a dye, and flavoring, suchas cherry or orange flavor. Of course, any material used in preparingany dosage unit form should be pharmaceutically pure and substantiallynon-toxic/biocompatible in the amounts employed. In addition, thepharmaceutical composition can be incorporated into sustained-releasepreparations and formulations.

Thus, a “pharmaceutically acceptable carrier” is intended to includesolvents, dispersion media, coatings, antibacterial and antifungalagents, isotonic and absorption delaying agents, and the like. The useof such media and agents for pharmaceutically active substances is wellknown in the art. Except insofar as any conventional media or agent isincompatible with the pharmaceutical composition, use thereof in thetherapeutic composition or the method of treatment is contemplated.Supplementary active compounds can also be incorporated into thecomposition.

In certain embodiments, the therapeutic method includes administeringthe composition topically, systemically, or locally as an implant ordevice. When administered, the therapeutic composition described by anembodiment is generally in a pyrogen-free, physiologically acceptableform. Further, the composition may desirably be encapsulated or injectedin a viscous form for delivery to the site of bone, cartilage or tissuedamage. Topical administration may be suitable for wound healing andtissue repair. Therapeutically useful agents other than the chimera ofan embodiment may also optionally be included in the composition asdescribed above, may alternatively or additionally, be administeredsimultaneously or sequentially with the chimera in the methods of thedescribed herein. For example, preferably for bone and/or cartilageformation, the composition would include a matrix capable of deliveringa BMP chimera or other therapeutic compounds to the site of bone and/orcartilage damage, providing a structure for the developing bone andcartilage and optimally capable of being resorbed into the body. Forexample, the matrix may provide slow release of the BMP chimera. Suchmatrices may be formed of materials presently in use for other implantedmedical applications.

The choice of matrix material is based on biocompatibility,biodegradability, mechanical properties, cosmetic appearance andinterface properties. The particular application of the subjectcomposition will define the appropriate formulation. Potential matricesfor the composition may be biodegradable and chemically defined calciumsulfate, tricalciumphosphate, hydroxyapatite, polylactic acid andpolyanhydrides. Other potential materials are biodegradable andbiologically well defined, such as bone or dermal collagen. Furthermatrices are comprised of pure proteins or extracellular matrixcomponents. Other potential matrices are non-biodegradable andchemically defined, such as sintered hydroxyapatite, bioglass,aluminates, or other ceramics. Matrices may be comprised of combinationsof any of the aforementioned types of material, such as polylactic acidand hydroxyapatite or collagen and tricalciumphosphate. The bioceramicsmay be altered in composition, such as in calcium-aluminate-phosphateand processing to alter pore size, particle size, particle shape, andbiodegradability.

Certain compositions disclosed herein may be administered topically,either to skin or to mucosal membranes. The topical formulations mayfurther include one or more of the wide variety of agents known to beeffective as skin or stratum corneum penetration enhancers. Examples ofthese are 2-pyrrolidone, N-methyl-2-pyrrolidone, dimethylacetamide,dimethylformamide, propylene glycol, methyl or isopropyl alcohol,dimethyl sulfoxide, and azone. Additional agents may further be includedto make the formulation cosmetically acceptable. Examples of these arefats, waxes, oils, dyes, fragrances, preservatives, stabilizers, andsurface active agents. Keratolytic agents such as those known in the artmay also be included. Examples are salicylic acid and sulfur.

It is especially advantageous to formulate a parenteral composition indosage unit form for ease of administration and uniformity of dosage.“Dosage unit form” as used herein, refers to physically discrete unitssuited as unitary dosages for the individual to be treated; each unitcontaining a predetermined quantity of pharmaceutical composition iscalculated to produce the desired therapeutic effect in association withthe required pharmaceutical carrier. The specification for the dosageunit forms of an embodiment are related to the characteristics of thepharmaceutical composition and the particular therapeutic effect to beachieve.

The principal pharmaceutical composition is compounded for convenientand effective administration in effective amounts with a suitablepharmaceutically acceptable carrier in an acceptable dosage unit. In thecase of the composition containing supplementary active ingredients, thedosage is determined by reference to the usual dose and manner ofadministration of the said ingredients.

One of the challenges to using a chimera as therapeutics is the abilityto deliver the proteins effectively. The chimera of an embodiment can bedelivered by several different methods. In the blood stream, thehalf-life of most TGF-β ligands is on the order of minutes. Tocompensate for the ligands being degraded so quickly, current therapiesinvolving TGF-β ligands use very high doses of the proteins.Alternatively, several means to directly modify the ligands or deliverysystems are available to help improve the stability or sustained releaseproperties of the ligands.

(1) Direct modification of the protein includes PEGylation as one commonform of modification. In this method, polyethylene glycol (PEG) iscovalently attached to the protein in hopes of improving stability byincreasing solubility, resistance to proteolysis, and decreasedimmunogenicity.

(2) Rational modification of residues on the protein surface. Byimproving any electrostatic instability, without changing overallprotein function, the overall stability of molecule can be improved.Using continuum electrostatic models, residues contributing toinstability can be located and then analyzed to see if it can be mutatedto a more favorable residue.

(3) Fusing the ligand to another protein or portion of a protein isanother technique to increase protein stability and solubility. Theantibody constant fragment (Fc) is common fusion partner used to improvethe stability and solubility.

(4) The use of liposomes can be used as a protein delivery vehicle.Liposomes are composed of any number of different phospholipids, whichself-assemble to form spheres. The protein of interest is encapsulatedinside the bilayer, protecting it from the outside environment. Thephospholipid composition influences the exact properties of the liposomeand can be tailored to release the protein under any number of desiredconditions. Polymer/liposome composite systems are also available to beused as delivery systems. Ideally, this type of system combines theadvantages of each system to improve protein delivery.

(5) Similar to liposomes, polymers can be used as protein drug deliverysystems. The polymers are used to make a matrix, commonly what is termeda hydrogel due to the high water content of the material. The advantageof using the gel is it allows for long term, sustained release as wellas protecting the protein from proteolysis. As with the liposomes, thepolymers used to make the gel influence its properties. There are twogeneral classifications for the materials used to make the hydorgels:natural and unnatural polymers. Common materials used to createhydrogels using natural polymers include collagen, gelatin, fibrin,Hyaluronic acid, alginate, chitosan, and dextran. Synthetic polymersused to make hydrogels include Poly(ethylene oxide), Poly(acrylic acid).Poly(N-isopropylacrylamide), Poly(vinyl alcohol), and Polyphosphazene.

(6) A different kind of hydrogel can be created without the use ofpolymers, either natural or unnatural. Considered to be a bioactiveglass, or Xerogel, this material is created from silica and calciumphosphate layer capable of absorbing the protein of interest. TheXerogel increases the sustained release time of the protein up to weeks.Results from cell viability assay using osteoblast cell line MC3T3 byMTT assay show that the xerogel material is nontoxic up to the highestconcentration of 30 mg/ml in the culture media we tested.

The chimeric polypeptide of an embodiment, alone or in combination, canbe used to treat a subject suffering from a liver disease (including,but not limited to, nonalcoholic fatty liver disease, liver fibrosis andhepatic inflammation) or a bone and cartilage disease (including, butnot limited to, osteoporosis, periodontal diseases, cartilage disorderand cartilage damage such as injury to the articular cartilage,osteoarthritis, costochondritis, herniation, achondroplasia, relapsingpolychondritis, benign or non-cancerous tumors, or malignant orcancerous tumors). The chimera of an embodiment can be used to promotebone and/or cartilage formation, inhibiting bone loss/density ordemineralization, promoting bone deposition and the like. Alternatively,the chimera of an embodiment can be used to inhibit excessive bonedensity and growth.

EXAMPLES Example 1

Description of Domains (Building Blocks) for Generating Designer Ligand

In order to create the chimera, a first step was deciding where to makethe borders for each of the domains. The chimera library has beenconstructed using activin-pA and BMP-6 as two sequence sources. Todesign the cut-off regions (Junction) for the domains to make theactivin/BMP-6 (AB) chimera, a structure-guided approach combined withprotein sequence alignment was used. Initially, the 3-dimensionalcrystal structures of activin-PA (Harrington et al., 2006) and BMP-6(Allendorph et al., 2007) were inspected structurally. From thisanalysis, the ligands were loosely divided into 6 distinct domains (seeFIG. 4 for domains 1 through 6). The exact domain junctions wereultimately determined following a protein sequence alignment of the twoligands to minimize any sequence changes of either protein sequence as aresult of joining the Junction. Further, the domain boundaries werechosen to be located in structural regions away from receptor bindingsites.

Detailed descriptions of Junctions: Between domains 1 and 2 (Junction1): Focusing on the boundary of domain 1 and domain 2, we found a10-residue region that is highly conserved between BMP-6 and activin-βA.Indeed, 8 of the 10 residues are identical and the other two are veryconservative differences. This area is located in the tip region ofFinger 1 and depending of the ligand, makes or is predicted to makelimited contacts with either receptor type. Based on the ternary crystalstructure of BMP2/BMPRIa/ActRII (Allendorph et al., 2006), only Val-26,Gly-27, and Trp-28 (BMP-2 numbering) generate contacts with the type Ireceptor. Of these three residues, only Val-26 is different between theligands, but it is a, very conservative change since the correspondingresidue in activin-βA and BMP-6 is Ile-23 and Leu-43, respectively.Since the residues in this region are very similar and not involved inreceptor binding, it makes for a good boundary point for domains 1 and2.

Between domains 2 and 3 (Junction 2): Moving to the boundary regionbetween domains 2 and 3, another good area for our boundary cut-off canbe found. Here exists a highly conserved region of 6 residues betweenactivin-βA and BMP-6, where 4 of the 6 residues are identical. When theligands are properly folded, this region is located in the center of thedimer, with both cyteines participating in the cysteine knot. This isadvantageous because the residues here are buried from the surface ofthe ligands and do not participate in any ligand-receptor interactions.

Between domains 4 and 5 (Junction 4): Similar to the domain 2/3boundary, the domain 4/5 boundary is situated in an excellent locationfor the cut-off. Here, we find a 6-residue region that is highlyconserved between activin-βA and BMP-6 with 4 identical residues out ofthe 6 residues, and this region is also buried at the center of theligand dimer. The 2 cysteine residues participate in both the cysteineknot as well as the inter-monomer disulfide bond. Again, this locationprevents the residues in this region from participating in receptorbinding interactions.

Between domains 5 and 6 (Junction 5): To extend the design of the BMP-6and activin-βA chimera, other boundary regions have been chosen tofacilitate generating RASCH constructs using all members of the TGF-βsuperfamily. Along with sharing structural architecture, the TGF-βsuperfamily ligands seem to have certain regions in their proteinsequences that are highly conserved. Interestingly, these regionscoincide with the boundary regions chosen for making the BMP-2 andactivin-βA chimera. For example, in the boundary region of 4 and 5, mostligands share 3 out of the 4 residues that define the boundary domain.This high degree of similarity, coupled with these regions beingisolated from the receptor binding sites, indicates RASCH as theuniversal strategy to create a library of Designer Ligands with newfunctionalities.

Between domains 3 and 4 ((Junction 3): The boundary between domains 3and 4 is subject to structural variability between differentsubfamilies, in which ligand-receptor assembly mechanism can differsubstantially. In certain embodiments, domains 3 and 4 may be treated asone segmental piece such that two domains will be derived from thecommon parental strand to preserve their structural integrity.

The structural similarity among all TGF-beta superfamily ligands formsthe rational basis for designing chimeric protein by exchanging(swapping) related domains of the sequences known to carry out certainfunctionality such as molecular recognition. Protein engineering ofAntibody chain, or more specifically of antibody fragment (Fab), will bea prime example where the basic structural scaffold is built on the Corearchitecture of the light- and heavy chain sequences, for which sixvariable loops, three from each of the two chains, are responsible forthe role of epitope-binding specificity. In the similar vein, theTGF-beta superfamily ligands share their structural framework as abutterfly-like architecture. A portion(s) of the sequence domainsfunctionally equivalent to variable loop regions of Antibody can then be‘implanted’ to transfer recognition specificity from one ligand toanother. Our design principle distinguishes itself from theaforementioned ‘functional transfer by sequence implantation’. The newchimeric library is created on the basis of structural feasibility ofeach domain as defined by each Junction. The junctions between thevarious domains of the TGF-beta family members used to generate thechimera of the disclosure provide useful building blocks of the chimeralibrary. By this reasoning. Junctions 1, 2, 4, and 5 are well defined tobe broadly applicable to all TGF-beta superfamily members, whereasJunction 3 is not broadly applicable. The application of Junction 3 inthe chimera design depends on the target sequences. The approachmaximizes the chance of producing such protein products that arefoldable, for which functional characterization will then follow.

Example 2

Generation of TGF-β Chimeras

To generate these novel TGF-β ligands, a modified directed evolutionapproach was utilized. Typically, this technique involves making a largenumber of random protein sequences, greater than 10³, either by mixingthe sequences of homologous genes or inserting random mutations and thenscreening for the desired ligand properties. Using a structure guidedapproach, several TGF-β ligand crystal structures were analyzed anddivided into 6 distinct domains. These domains roughly encompass thefollowing regions of the ligand: domain 1, N-terminus and beta strand 1;domain 2, beta strand 2; domain 3, pre-helix loop; domain 4, alphahelix; domain 5, beta strand 3; and domain 6, beta stand 4 andC-terminus. Using this protocol, 64 different ligand combinations arepossible for each set of TGF-β ligands chosen to be recombined. When twoor more parental chains are from different subfamilies (e.g. BMP/GDFv.s. TGFbeta), the difference between their signaling mechanisms may notbe captured if domains 3 and 4 are separated. To be broadly applicableas the design principle, it is also part of the design to keep twostructural domains, domains 3 and 4, can be treated as one domain ofeither of the parental gene (referred to as domain 3*4).

The strategy was implemented by making an activin/BMP-6 chimera, whereActivin-βA was picked as the target ligand as it has high affinity toTGF-β type II receptors. BMP-6 was chosen as it is biologically veryinteresting. To design the various domains, a sequence alignment ofBMP-6 and activin-βA was performed to locate regions of sequenceidentity between the ligands (FIG. 4). These regions were used as theboundaries for the different domains. By using these parts of thesequence as the overlap regions for the oligonucleotides during PCR,changes will not be introduced into either the BMP-6 or activin-βAsequences. The sequence alignment was then used in conjunction with datafrom previously solved BMP-6 and activin-βA structures to ultimatelydetermine the 6 domains (FIG. 4 a-c). Due to limitations with regions ofidentity between the sequences, the domains had to be shifted slightlyfrom ideal. Particularly, the pre-helix loop and the majority of theα-helix were combined into one domain, while the remainder of theα-helix to the beginning of beta strand 3 was placed into a differentdomain (FIGS. 4 b and c).

The chimeras are labeled according to the domains they contain. Forexample, 1b2b3b4a5a6b, in which the b's represent that the domain istaken from BMP-6 and the a's represent that the domain is derived fromactivin-βA.

One of the activin/BMP-6 chimeras, designated as AB604 (SEQ ID NO: 12)is shown in FIG. 5. (SEQ ID NO:11 shows DNA sequence of AB604.)

Example 3

Protein Expression and Purification

The activin/BMP-6 chimeras were expressed using a typical E. coliexpression system using E. coli BL21(DE3), and the chimeras were foundin the inclusion body fractions. The expressed inclusion bodies wereisolated, purified, and refolded. The refolded ligands were purified byreversed phase chromatography (GraceVydac). The ligands were lyophilizedand re-suspended in 1 mM HCl for use in all cell based assays or 10 mMNa acetate, pH 4 for all biophysical assays. Activin-PA was expressed ina stably transfected CHO cell line and purified using techniques knownin the art.

One of the activin/BMP-6 chimeras, designated as AB604 is shown in FIG.5. AB604 proteins in inclusion bodies were seen as single bands on areduced, SDS-PAGE gel and found at the expected size of about 15 kDa(FIG. 6; lanes labeled “R”), which means that AB604 exists as monomersin the inclusion bodies. AB604 was refolded in 600 mL volumes at aconcentration of 50 mg/L, 100 mg/L or 200 mg/L. After refolding singlebands were seen on a non-reduced, SDS-PAGE gel and found at the expectedsize of about 30 kDa (FIG. 6; lanes labeled “NR”), which means thatAB604 exists as dimers after successful refolding. The concentration waschosen based on previously successful BMP-2 and AB204 refoldings.

After refolding, activin/BMP-6 chimeras were purified using Agilent HPLCsystem with Vydac C4 column (10×250 mm). Purified activin/BMP-6 chimeraswere confirmed as disulfide-bonded dimers on a reducing or non-reducingSDS-PAGE gel (FIG. 7).

AB604 showed higher yield than AB204 (one of activin/BMP-2 chimeras).Refolding step is the critical step during production that determinesthe overall yield of activin/BMP chimera proteins. Thus, the yield wascalculated as the amount of successfully refolded proteins in 1 L ofrefolding volume. The yield of AB604 is 50 mg/L, which is 10-fold higherthan the yield of AB204 (TABLE 3).

TABLE 3 AB604 AB204 Refolding Volume 600 mL 200 L Amount of therecovered protein after 120 mg 50 g refolding Purified amount 30 mg 1 gYield(Basis: 1 L refolding volume) 50 mg/L 5 mg/L

Example 4

Smad-1 Signaling Activity

To be considered a successful ligand, the activin/BMP-6 chimeras notonly have to be refoldable but they also need to display signalingcharacteristics. To test for these properties, activin/BMP-6 chimeras,regardless of refolding efficiency, were initially subjected tosignaling activity assays. BMP-like signaling characteristics weretested using a whole cell luciferase reporter assay sensitive to Smad-1signaling activation (as described below). It was previously shown thatBMP-2 shows higher Smad-1 signaling activity compared to BMP-6 (FIG. 3).AB604 showed higher activity than BMP-6, and surprisingly even higheractivity than BMP-2 as well (FIG. 8).

Furthermore, Smad-1 signaling activity of AB604 was 7-fold stronger thanthat of AB204 in terms of EC₅₀ values (FIG. 9).

Smad-1 Luciferase Assays in C2C12 Cells were performed as the following.Smad1-dependent luciferase assays were performed using techniques knownin the art. In brief, C2C12 myoblast cells are cultured in Dulbecco'sminimum essential medium (DMEM)+10% FBS supplemented with L-Glutamineand antibiotics. For luciferase reporter assays, cells were trypsinized,washed twice with PBS and plated into 96-well plates with OptiMEMcontaining 1.0% FBS. Then, cells were transfected with1147Id1-luciferase construct containing the Smad binding sites(Id1-Luc), a Smad1 expression construct, and a CAGGS-LacZ plasmid byusing Fugenc6 (Roche) according to the manufacturer's instruction andcells were stimulated with increasing amounts (0.4 ng/ml, 1.2 ng/ml, 3.7ng/ml, 11 ng/ml, 33 ng/ml, 100 ng/ml, 333 ng/ml, 1,000 ng/ml, 3, 333ng/ml, and 10,000 ng/ml) of BMP-6, BMP-2 or activin/BMP-6 chimeras added24 hours post transfection. Luciferase activity was measured 16 hoursafter stimulation with ligands and the values were normalized fortransfection efficiency by using beta-galactosidase activity.

Example 5

Smad-2 Signaling Activity

Since activin/BMP6 chimeras also contain sequences of activin A,activin-like signaling characteristics of activin/BMP-6 chimeras weretested using a whole cell luciferase reporter assay sensitive to Smad-2signaling activation (as described below). TGFβ1 was used as a positivecontrol since it is well known that TGFβ1 has Smad-2 signaling activity.AB604 showed almost no signaling activity in Smad-2 signaling pathway,in which TGFβ1, however, exhibited its activity as expected (FIG. 10).In summary, AB604, one of the activin/BMP6 chimeras, consisting ofsequences of activin A and BMP6, inherited its signaling property fromBMP6, but not from activin A.

Smad-2 Luciferase Assays in HEK293T cells were performed as thefollowing. Smad2-dependent luciferase assays were performed usingtechniques known in the art. In brief, HEK293T cells are cultured inDulbecco's minimum essential medium (DMEM)+10% FBS supplemented withL-Glutamine and antibiotics. For luciferase reporter assays, cells weretrypsinized, washed twice with PBS and plated into 96-well plates withOptiMEM containing 1.0% FBS. Then, cells were transfected with A3 Luxconstruct containing three repeats of activing response elements (ARE),a FAST2 expression construct, and a beta-galactosidase expressionplasmid using Fugene6 (Roche) according to the manufacturer'sinstruction and cells were stimulated with increasing amounts of ligands(for example, 0.01 ng/ml, 0.1 ng/ml, 1.0 ng/ml, 10 ng/ml, 100 ng/ml ofAB604 or 0.0005 ng/ml, 0.005 ng/ml, 0.05 ng/ml, 0.5 ng/ml, 5 ng/ml, 50ng/ml, and 500 ng/ml of TGFβ1) added 24 hours post transfection.Luciferase activity was measured 16 hours after stimulation with ligandsand the values were normalized for transfection efficiency by usingbeta-galactosidase activity.

Example 6

Inhibition of TGFβ Signaling

AB604 was shown to inhibit the signaling activities of TGFβ1 morepotently than BMP6 in HEK293T cells as observed by a luciferase reporterassay. When TGFβ1-responsive A3 promoter was activated by TGFβ1 inHEK293T cells in the presence or absence of BMP6 or AB604 at variousconcentrations, the maximally attainable signaling activity by TGFβ1 wassuppressed by the presence of BMP6 or AB604 in a dose-dependent manner(FIG. 11 to FIG. 14). This suppressive effect was more prominent byAB604 than by BMP6. For example, FIG. 12 and FIG. 14 show dose-dependentdecreases of TGFβ1-mediated luciferase activities by BMP6 and AB604,respectively. AB604 displayed a statistically significant reduction ofTGFβi activities already at 1 ng/ml (FIG. 12), whereas BMP6 did so at100 ng/ml (FIG. 14)

Example 7

Noggin Sensitivity

BMP2 signaling is regulated by a natural antagonist noggin, which bindsBMP2 and prevents it from binding to its cognate receptors on cellmembranes. BMP6 is known to be weakly inhibited by noggin.BMP-responsive luciferase reporter assay in C2C12 cells was used to seewhether AB604 is sensitive to noggin or not. C2C12 cells weretransiently transfected with Id1-luc, Smad1, and β-galactosidase andthen treated with BMP2, BMP6, or AB604 at various concentrations withthe indicated molar ratio of noggin supplemented. All of BMP2, BMP6, orAB604 exhibited dose-dependent increases of luciferase activities (FIG.15), but the suppression of the activity by noggin was only observed inBMP2 (FIG. 15A). The activities of BMP6 or AB604 was not significantlyaffected by noggin, suggesting noggin-insensitivity of both BMP6 andAB604.

Example 8

Activation of Hepcidin Gene Expression

BMP6 regulates the expression of hepcidin in hepatocytes. Hepcidin isknown as a master regulator of systemic and hepatic iron homeostasis, byits action of degrading ferroportin (FPN), an iron-efflux transporter incell membranes. The effects of BMP6 and AB604 in inducing hepcidin geneexpression were tested in Hep3B and HepG2 cells. Both BMP6 and AB604have increased mRNA level of hepcidin significantly in both Hep3B cellsand HepG2 cells, compared to the control. Moreover, the increase of mRNAlevel of hepcidin was significantly greater in AB604-treated cells thanBMP6-treated counterparts (FIG. 16). The dose-dependent profile ofhepcidin gene expression demonstrated the higher potency of AB604compared to that of BMP6, where EC50 values of BMP6 and AB604 exhibited3-fold differences (12.89 ng/ml for BMR6, 4.42 ng/ml for AB604) (FIG.17).

Example 9

Phosphorylation of SMAD Proteins

Signaling of TGFβ superfamily ligands involves SMAD proteins incytoplasm. For example, BMP6 phophorylates SMAD1/5/8 and Activin A orTGFβ1 phophorylate SMAD2/3, SMAD1/5/8 refers to SMAD1, SMAD5, or SMAD8,and SMAD2/3 refers to SMAD2 or SMAD3. Once phosphorylated, thesereceptor SMADs (R-SMAD) such as SMAD1/5/8 or SMAD2/3 form complex withCo-SMAD or SMAD4, and subsequently go into nucleus to regulateexpression of specific target genes. Which SMAD proteins arephosphorylated by AB604 was confirmed by western blot analysis in threedifferent cell lines; C2C12, HEK293T, and HepG2. Cells were treated withTGFβ1, BMP6, or AB604 for 30 minutes or 60 minutes, and thenphosphoSMAD1/5/8 or phospho-SMAD2 levels were visualized by westernblot. AB604 treatment led to a strong phosphorylation of SMAD1/5/8 inall three cell lines. However, BMP6 showed less prominentphosphorylation of SMAD1/5/8 in C2C12 or HEK293T cells, compared toAB604, and almost did not phosphorylate SMAD1/5/8 in HepG2 cells. TGFβ1also showed some degree of phosphorylation in C2C12 cells, but not inother cell lines. Taken together, AB604 causes the most significantlevel of SMAD1/5/8 phosphorylation (FIG. 18). On the other hand, SMAD2phosphorylation was strong by TGFβ1 in all three cell lines.Interestingly, AB604 was also able to phosphorylate SMAD2 only inHEK293T cells (FIG. 19).

The invention claimed is:
 1. A polypeptide capable of binding to one ormore of Transforming Growth Factor-beta (TGF-β) superfamily members; orone or more of TGF-β receptors, and comprising the sequence of SEQ IDNO:12.
 2. A homo-dimer of the polypeptide of claim 1.